Here is the code for my computed field:
$node_field['value'] = $node->taxonomy[tags] ." ". $node->title;
So in the end my field should look like this: [taxonomy term] [title]
This field updated correctly if I edit the node and then re-save it. Upon using your module on 57,000+ nodes, each one shows up as just [title]. So it actually did compute the field (otherwise it would be blank), it just computed it incorrectly and didn't pull the taxonomy for some reason. Trying again resulted in 57,000 "duplicate entry" errors.