We all use Debian as desktop and as server. We are webprovider and all our machines are running Debian. At last we made a Sarge-update.
The main software on all desktops is Firefox version 1.5 and Thunderbird. For programming we use ZEND, it works very well. But also multimedia tools like XMMS and realplayer are in use. My best designs I create with my beloved GIMP. I've used Debian for nearly 5 years, my partner too.
We have a lot of machines, and we never had problems with Debian. No crashes, no hangs! During the time using Debian, we have had to reinstall the secretaries Windows desktop 20 times. We also tried SuSE, Mandrake and Red Hat, but like Windows, they too have become similar to playstations.
The completely working APT is nice, because the latest software is always available on PC, which I've never seen on a Windows PC at this price! :D
Personally I would never use another platform, also I would never accept another platform on our servers. Debian machines run forever.