In August, I've filed a Feature Request and suggested to allow logging into database tables additionally to writing log files to the file system. The development is in progress and it's told that the feature will probably be available in one of the earlier 5.1 releases.
We also know, that in MySQL 5.1.6 the Event Scheduling Feature will be available - read more about it here: http://dev.mysql.com/tech-resources/articles/event-feature.html
The combination of these two new features will give great new possibilities. The log data will be available more conveniently and it will also be very easy to filter those records that are of interest (with simple SQL statements). The Event Scheduling Feature can be run at regular intervals to filter out particular records, or to accumulate data - all possible kinds of things. This way it will be much easier and more comfortable for DBAs to find out, what's exactly going on on the MySQL server.