For a long time in Gentoo, if I had the "Use my KDE style in GTK applications" option selected in KDE, certain themes would cause all GTK apps to fail to even start. Only certain QT themes did it though. Domino for example, which happens to be my favorite QT app.
I also had some redraw problems with GTK apps no matter what QT theme I used. When changing between virtual desktops, bits and pieces of certain GTK apps wouldn't redraw properly until I moved them around or resized them. And as I mentioned an entry or two ago, I had some lag problems when switching between desktops in general. Nothing show-stopping. Just barely bad enough to annoy me at times.
Strangely, all of those problems seem to have been corrected. Must've been something fixed in the past month. Or maybe something on my system was b0rked and the slew of updates that accumulated over the past month caused me to have to recompile something that fixed it. That included a new version of xorg, tons of KDE apps, a new nvidia driver, and lots of other things, and I upgraded freetype to the latest keyworded version. I wish I knew what it was in particular that fixed things so well. Such are the mysteries of Gentoo.