The switch user block should user format_username(), which requires full user objects

'title' => check_plain(format_username($account)),

won't that give you entity coded A tag with brackets and such? i can't think of an alternative though.

Maybe something like check_plain(decode_entities(strip_tags(format_username($account))))?

Isn't what we see above between "Posted by" and "on December 12" the result of format_username()?

Tested and committed, thanks!

+++ devel.module	12 Dec 2010 17:13:32 -0000
@@ -728,23 +728,28 @@ function devel_switch_user_list() {
     $roles = user_roles(TRUE, 'switch users');
...
+      $or_condition->condition('r.rid', array_keys($roles), 'IN');

Upon initial installation, $roles is empty

=> Fatal error and nice WSOD. :(

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More specifically:

PDOException: SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')) ) ORDER BY u.access DESC LIMIT 10 OFFSET 0' at line 2: SELECT DISTINCT u.uid AS uid FROM {users} u LEFT OUTER JOIN {users_roles} r ON u.uid = r.uid WHERE (u.uid > :db_condition_placeholder_0) AND (u.status > :db_condition_placeholder_1) AND( (u.uid = :db_condition_placeholder_2) OR (r.rid IN ()) ) ORDER BY u.access DESC LIMIT 10 OFFSET 0; Array ( [:db_condition_placeholder_0] => 0 [:db_condition_placeholder_1] => 0 [:db_condition_placeholder_2] => 1 ) in devel_switch_user_list() (line 747 of sites/all/modules/devel/devel.module).

note the empty

OR (r.rid IN ()) )

This should do the trick.

Tested, works.