I was using KDE until it broke me down with its poor networking (you cannot open+save an Openoffice document from/to the network), then I switched to Gnome + Compiz Fusion which is actually quite good but a little bit unstable sometimes (at least with the open source ATI driver).

I watched a video introducing Gnome3 and its new features and read an excellent article about its basics. I gave it a try by installing Fedora15 on my home desktop and laptop.