Honestly, I don't think there's any compelling reason to switch from the DE you are most familiar with right now (Gnome to KDE or vice versa). Functionality-wise, KDE and Gnome are pretty similar to each other, with the differences being mostly cosmetic. (Oops, now I've done it. Preemptive agreement: yes, Qt is like 100m times better than GTK, and no there's
no comparison between KDESC's media player - I forget its name - and Rythmbox/Banshee and
yes Gnome is infected with the Mono crap and we shouldn't use it

).