Simplicity and speed, first and foremost. Our bug records are extremely simple. Bugs have an ID number, a one-line summary, a description, a creation/modification/close date, a status (open or closed), a severity (only 4 levels), an owner, the version filed against, the version targeted for resolution, and that’s pretty much it.
A lot of trackers go way, waaay too overboard with the fields. We need to work on bugs, not placate a needy database.