diff -urp drupal-5.1/modules/comment/comment.module drupal-5.1-patched/modules/comment/comment.module
--- drupal-5.1/modules/comment/comment.module	2007-01-29 15:51:53.000000000 -0600
+++ drupal-5.1-patched/modules/comment/comment.module	2007-05-19 16:06:24.000000000 -0500
@@ -1948,6 +1948,7 @@ function _comment_update_node_statistics
   if ($count > 0) {
     $last_reply = db_fetch_object(db_query_range('SELECT cid, name, timestamp, uid FROM {comments} WHERE nid = %d AND status = %d ORDER BY cid DESC', $nid, COMMENT_PUBLISHED, 0, 1));
     db_query("UPDATE {node_comment_statistics} SET comment_count = %d, last_comment_timestamp = %d, last_comment_name = '%s', last_comment_uid = %d WHERE nid = %d", $count, $last_reply->timestamp, $last_reply->uid ? '' : $last_reply->name, $last_reply->uid, $nid);
+    db_query('UPDATE {comments} SET last_comment_timestamp = %d WHERE nid = %d', $last_reply->timestamp, $nid);
   }
 
   // no comments
diff -urp drupal-5.1/modules/system/system.install drupal-5.1-patched/modules/system/system.install
--- drupal-5.1/modules/system/system.install	2007-01-10 17:22:34.000000000 -0600
+++ drupal-5.1-patched/modules/system/system.install	2007-05-19 16:30:50.000000000 -0500
@@ -3508,6 +3508,28 @@ function system_update_1021() {
  * @} End of "defgroup updates-4.7-to-5.0"
  */
 
+/**
+ * Update indexes and table structure for new tracker.
+ */
+function system_update_1022() {
+  $ret = array();
+  switch ($GLOBALS['db_type']) {
+    case 'mysql':
+    case 'mysqli':
+      $ret[] = update_sql('ALTER TABLE {comments} ADD last_comment_timestamp INT(11) NOT NULL');
+      $ret[] = update_sql('ALTER TABLE {comments} DROP INDEX tracker_user, ADD INDEX tracker_user (uid, status, last_comment_timestamp)');
+      $ret[] = update_sql('ALTER TABLE {comments} DROP INDEX tracker_global, ADD INDEX tracker_global (status, last_comment_timestamp)');
+      $ret[] = update_sql('ALTER TABLE {node} DROP INDEX tracker_user, ADD INDEX tracker_user (uid, status, changed)');
+      $ret[] = update_sql('ALTER TABLE {node} DROP INDEX tracker_global, ADD INDEX tracker_global (status, changed)');
+      $ret[] = update_sql('UPDATE {comments} c SET last_comment_timestamp = (SELECT last_comment_timestamp FROM {node_comment_statistics} l WHERE l.nid = c.nid)');
+      break;
+    case 'pgsql':
+      // TODO: PostgreSQL updates
+      break;
+  }
+  
+  return $ret;
+}
 
 /**
  * @defgroup updates-5.0-to-x.x System updates from 5.0 to x.x
Only in drupal-5.1-patched/modules/tracker: .DS_Store
diff -urp drupal-5.1/modules/tracker/tracker.module drupal-5.1-patched/modules/tracker/tracker.module
--- drupal-5.1/modules/tracker/tracker.module	2007-01-10 09:17:51.000000000 -0600
+++ drupal-5.1-patched/modules/tracker/tracker.module	2007-05-19 16:03:38.000000000 -0500
@@ -70,30 +70,104 @@ function tracker_track_user() {
 }
 
 /**
+ * Hack to allow manual updates to pager statistics and slice up the pages.
+ */
+function _tracker_pager_update($results, $limit = 10, $element = 0) {
+  global $pager_page_array, $pager_total, $pager_total_items;
+  $page = isset($_GET['page']) ? $_GET['page'] : '';
+  $pager_page_array = explode(',', $page);
+
+  // We calculate the total of pages as ceil(items / limit).
+  $pager_total_items[$element] = count($results);
+  $pager_total[$element] = ceil($pager_total_items[$element] / $limit);
+  $pager_page_array[$element] = max(0, min((int)$pager_page_array[$element], ((int)$pager_total[$element]) - 1));
+
+  // Return only results for the current page
+  return array_slice($results, $pager_page_array[$element] * $limit, $limit);
+}
+
+/**
  * Menu callback. Prints a listing of active nodes on the site.
  */
 function tracker_page($uid = 0) {
   // Add CSS
   drupal_add_css(drupal_get_path('module', 'tracker') .'/tracker.css', 'module', 'all', FALSE);
 
-  // TODO: These queries are very expensive, see http://drupal.org/node/105639
+  // Only restrict to a uid if one is provided
+  $node_uid_condition = '1';
+  $comment_uid_condition = '1';
   if ($uid) {
-    $sql = 'SELECT DISTINCT(n.nid), n.title, n.type, n.changed, n.uid, u.name, GREATEST(n.changed, l.last_comment_timestamp) AS last_updated, l.comment_count FROM {node} n INNER JOIN {node_comment_statistics} l ON n.nid = l.nid INNER JOIN {users} u ON n.uid = u.uid LEFT JOIN {comments} c ON n.nid = c.nid AND (c.status = %d OR c.status IS NULL) WHERE n.status = 1 AND (n.uid = %d OR c.uid = %d) ORDER BY last_updated DESC';
-    $sql = db_rewrite_sql($sql);
-    $sql_count = 'SELECT COUNT(DISTINCT(n.nid)) FROM {node} n LEFT JOIN {comments} c ON n.nid = c.nid AND (c.status = %d OR c.status IS NULL) WHERE n.status = 1 AND (n.uid = %d OR c.uid = %d)';
-    $sql_count = db_rewrite_sql($sql_count);
-    $result = pager_query($sql, 25, 0, $sql_count, COMMENT_PUBLISHED, $uid, $uid);
+    $node_uid_condition = 'n.uid = %d';
+    $comment_uid_condition = 'c.uid = %d';
   }
-  else {
-    $sql = 'SELECT DISTINCT(n.nid), n.title, n.type, n.changed, n.uid, u.name, GREATEST(n.changed, l.last_comment_timestamp) AS last_updated, l.comment_count FROM {node} n INNER JOIN {users} u ON n.uid = u.uid INNER JOIN {node_comment_statistics} l ON n.nid = l.nid WHERE n.status = 1 ORDER BY last_updated DESC';
-    $sql = db_rewrite_sql($sql);
-    $sql_count = 'SELECT COUNT(n.nid) FROM {node} n WHERE n.status = 1';
-    $sql_count = db_rewrite_sql($sql_count);
-    $result = pager_query($sql, 25, 0, $sql_count);
+  
+  // Set a limit for the overall result set. Calculating the full, actual size requires creating the full result set, which is too expensive.
+  $sanity_limit = variable_get('tracker_limit', 1000);
+
+  // Find the latest nodes created by the user
+  $nodes_sql = 'SELECT n.nid, n.title, n.type, n.changed, n.uid, n.changed AS last_updated FROM {node} n WHERE n.status = 1 AND ' . $node_uid_condition . ' ORDER BY last_updated DESC';
+  $nodes_sql = db_rewrite_sql($nodes_sql);
+  // DISTINCT() causes the query to require a temporary table, and it doesn't matter much if we get duplicates here, anyway
+  // The process of combining the result sets will remove duplicates
+  $nodes_sql = str_replace('DISTINCT(n.nid)', 'n.nid', $nodes_sql);
+  $node_results = db_query_range($nodes_sql, $uid, 0, $sanity_limit);
+  
+  // Find the latest comments created by the user
+  $comments_sql = 'SELECT n.nid, n.title, n.type, n.changed, n.uid, c.last_comment_timestamp AS last_updated FROM {node} n INNER JOIN {comments} c ON n.nid = c.nid WHERE n.status = 1 AND c.status = %d AND ' . $comment_uid_condition . ' ORDER BY last_updated DESC';
+  $comments_sql = db_rewrite_sql($comments_sql);
+  // The same problem with DISTINCT() occurs here
+  $comments_sql = str_replace('DISTINCT(n.nid)', 'n.nid', $comments_sql);
+  $comment_results = db_queryd($comments_sql, COMMENT_PUBLISHED, $uid, 0, $sanity_limit);
+  
+  // Combine the results while avoiding duplication
+  $results = array();
+  $node = db_fetch_object($node_results);
+  $commented_node = db_fetch_object($comment_results);
+  while ($node || $commented_node) {
+    // Make sure we have the most recent node that's not currently listed
+    while (isset($results[$node->nid])) {
+      $node = db_fetch_object($node_results);
+    }
+    // Make sure we have the most recent commented node that's not currently listed
+    while (isset($results[$commented_node->nid])) {
+      $commented_node = db_fetch_object($comment_results);
+    }
+
+    // In the case where both exist
+    if ($node && $commented_node) {
+      // ...and the node was updated last
+      if ($node->last_updated > $commented_node->last_updated) {
+        $results[$node->nid] = $node;          
+      }
+
+      // ...and the comment was updated last
+      else {
+        $results[$commented_node->nid] = $commented_node;
+      }
+    }
+    // Case where only $node is set
+    else if ($node) {
+      $results[$node->nid] = $node;
+    }
+    // Case where only $commented_node is set
+    else if ($commented_node) {
+      $results[$commented_node->nid] = $commented_node;
+    }
   }
+  
+  // Update the pager and get the current page's results
+  $results = _tracker_pager_update($results, 25);
 
   $rows = array();
-  while ($node = db_fetch_object($result)) {
+  $names = array();
+  foreach ($results as $node) {
+    // Load these data here (instead of in a JOIN) to only load data for the current page
+    $node->comment_count = db_result(db_query('SELECT comment_count FROM {node_comment_statistics} WHERE nid = %d', $node->nid));
+    if (!isset($names[$node->uid])) {
+      $names[$node->uid] = db_result(db_query('SELECT name FROM {users} WHERE uid = %d', $node->uid));
+    }
+    $node->name = $names[$node->uid];
+    
     // Determine the number of comments:
     $comments = 0;
     if (module_exists('comment') && $node->comment_count) {