I seem to keep having this conversation. :D
I often find it difficult to describe my love for KDE. I've used GNOME, WindowMaker, Enlightenment, Xfce and even CDE for a time. KDE will suck on your RAM more than the others will, most likely, but on a modern PC the only time I would need a GUI and all of my RAM for my PC to be responsive is if I were running VMs configured in a cluster on it. KDE is a pleasant environment that allows you, more than any other environment, to configure your workspace precisely to how you want to do business with your PC.
On a typical day on my PC I'm running: Firefox, Konqueror (for google searches, via krunner), Yakuake (always in memory, drop-down console), Eclipse, Kate, Dolphin (often on multiple desktops), Kopete (IM client), Konversation (IRC client), GIMP, OpenOffice/Kword (depending on what I'm doing), Amarok (music rules), VLC, Kontact (groupware software, mostly for KMail), etc., etc.
I have a 3.2Ghz processor and 4GB or RAM which I don't even fully use (32 bit Ubuntu, I suck at making the big leap) and some kind of Nvidia card that plays WoW well (and I run that via Wine with -opengl) that allows me to have crazy desktop effects that run as smoothly as the first time I ran WindowMaker on my P133.
Times are changing, the desktop is on Linux now too. I don't think it will ever be for everybody but Linux has the best UI configuration capability, in my opinion, over any other PC interface I've ever used; here's the kicker, it's because of KDE for me. GNOME has always kind of had ups and downs with respect to philosophy regarding applications and how the UI is laid out for each. All KDE apps, unless the author took the pain to build it piece by piece themselves, are pretty much uniform in presentation and usage. GNOME can't claim that and everything else is pretty much just a window manager.
Robustness is not bad if you feel you actually need it. Stick with what works for you, KDE works for me. Open source is about options, too.