New version 0.4 of the Log Deprecated Calls plugin.
Now it has an option to toggle logging to the PHP Log, or a table in the database, or both. If logging to the database you can view the records on the admin page (under Plugins->Deprecated Calls. It also has a test function, and if you’re using WordPress 2.7 or up, it will even clean up after itself if you delete it.
Again, this is primarily of use to those who write plugins and themes.