A big problem was always the webbrowser. Now we have rekonq which is really good but it's still quite buggy. Another programm is gimp. I couldn't find a real competitor on the qt side (krita is basically a different audience).
Another way is to live with gtk+ applications is to use a widget style which works for both gtk+ and kde/qt, but i actually never liked the qtcurve widget style at all.
Recently i found another widget style which is called oxygen-gtk. This is the official port of kde's widget style to gtk+.
Well this one looks really good and makes my desktop much more "pure kde" :)
In gentoo's case you just have to:
emerge -av x11-themes/oxygen-gtk
Afterwards go into System-Settings --> Application Appearance --> Gtk Config. There you set the Theme to "oxygen-gtk".
The Result looks something like this (in the picture you see Gimp)