I avoid gtk applications as far as I can. I think Gnome is a pretty poor immitation of something akin to the OS X interface. It has some really strange quirks, even in the (much nicer) Ubuntu implementation. I find Gnome gets in my way more often than it's helping me to work faster.
Unfortunately two of the apps I use heavily - Firefox and Pidgin - are still based on GTK. It would be a great day when I can compile both with QT or something else.
Not that KDE is perfect but its UK design to me makes a lot more sense (even if it draws heavily on the Windows way) and it stays out of my way. My biggest complaint is that, if I start up a single Gnome application under KDE, it fires up all the gnome services in the background, which causes stupid situations like being unable to eject a USB flash drive because some gnome-vfs or something is hogging it. Under Ubuntu 10.10, opening Evolution crashes the KDE panel - tested on a few machines.