Custom Status Ajax not working after 1.6.5?

[ZiNgA BuRgA]

The only sure way is to go through all the code and see what it adds, and reverse it.
Otherwise, you really do have to trust that the uninstaller works.

If it's throwing SQL errors, you can try pushing it through, eg by adding a 'custom_status' column to your users table.  No guarantee that it'll remove everything, but you could try it...
Just make sure you have a backup.