Praveen says that GNOME is better but I don't think I will switch from KDE anytime soon. I know this is the start of a holy war, in spite of that, here is why I prefer KDE over GNOME :
Lots of good applications - Kate, Konsole, Quanta Plus, K3B, KSysGuard, Cervisia, KSnapshot, and many many more. Show me some reasonably good equivalents in the GNOME world. I've come across none.
Konqueror rocks - A web browser, file explorer, FTP client, manpage viewer, etc, etc all rolled into one.
Integration - Because of the KPart system, I can view zip files or read text within Konqueror and without the need to open another application. Also, all settings can be changed from a single Control Center.
OK and Cancel buttons are in the right order - yes, this is a serious usability issue for me.
IMHO, KDE is faster and more stable than GNOME. Also, Qt applications tend to be more lightweight and more stable than Gtk applications. For example, compare Kontact and Evolution, KDevelop and Anjuta, and the best comparison of all, Konsole and gnome-terminal.
KDE works well on FreeBSD whereas GNOME comes lacking in this respect. I know this doesn't particularly apply to me but in a company like Y! where almost all of the developers are on FreeBSD, this matters.
Upcoming KDE 4 will make you switch back to KDE. Period.
So, all ye Linux and BSD users, which is your choice?
Conclusion: The Free and Open Source Software community is all about choice. Its a good thing (TM) that we have choices - KDE, GNOME, XFCE, Enlightenment, etc. You can choose what you like and use it. Freedom to choose matters.