I used to be a huge fan of the GIMP, but gave up at 2.6 when I moved to a Mac: the OSX port was horrible, the drawing cursor would trail the mouse pointer by a second or two. The last version I really enjoyed using was 2.4.7 in 2007, after that, it just got a bit bloaty for me, although singe window mode sounds like a great step forward.
I may just give it another go.