I have been working in BBEdit a lot lately, with 20+ documents open at a time. I have found that after several hours of editing, BBEdit would become sluggish. Just about anything I would try to do (find and replace, cut and paste, even just typing) would be met by a a roughly one-second delay before the action would take place.
One of many ways in which BBEdit Doesn't SuckĀ® is that it has a remarkably long undo history. If you've got 20+ documents undergoing heavy editing, by the end of the day, that undo history is getting a little weighty (computationally speaking).
The Fix: Select 'Clear Undo History' from the Edit menu. Presto, no more slowdowns...
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050829003547791