I don't think so, really. My impression is that the LimeWire developers are more the emacs/vi type programmers who occasionally use eclipse but who don't spend money on fancy Swing IDEs. (Judging from the way the GUI code looks I'd say it's all good old typing and a certain amount of copy&paste).

Personally, I think it's not worth the trouble when editing a relatively simple GUI as LimeWire's, so if I'm modifying the LimeWire GUI code, I usually take emacs or jEdit.