I use KDE4 and Gnome interchangeable and I like them both.
One immediate thing that you'll notice once you shift to KDE4 is that the gtk2 applications like Gimp, VLC, Firefox and Eclipse don't look the way they should.
Here let me show you how to make KDE and gtk applications look consistent and look good.
1. Download gtk-kde4. Alternatively, download the binary package.
2. Extract the contents into some folder. Fire your terminal, change to that folder and copy certain files from the extracted package to the KDE base folder. On my system, the kde4 path is "/usr/lib/kde4". To locate KDE path, just do
$ locate /lib/kde4
$ sudo cp kcm_gk4.so /usr/lib/kde4/lib/kde4/
$ sudo cp kcm_gk4.desktop /usr/lib/kde4/share/kde4/services/
$ sudo cp gk4icon.png /usr/lib/kde4/share/icons/
3. Launch systemsettings and click on "Appearance" under the General tab
4. You'll find a new section for GTK style. Select your favorite style and click on apply.
5. Now launch your favorite gtk2 apps and see the difference!
Have fun with KDE4 !