Komodo remains responsive
I tried Komodo, but found it to be just a little less responsive than I liked. I think it's a great IDE, and they've got very smart people working on it, but my guess is that the single largest complaint they get about it is speed.
I've read it's written using some Mozilla-related thing called XUL, though I'm not familiar with XUL. I figure this was done to make Komodo cross-platform. Makes me wonder if ActiveState could've successfully built it using GTK or Qt, or if it would've taken far to long to implement in C or C++...