I've recently fully switched to developing exclusively on Linux as my desktop environment. I've always enjoyed some of the benefits when working under Linux, but after the past 7 months, I've noticed a substancial increase in productivity.
I started in Ubuntu 8.04, but never fully commited. Revisited the idea in Ubuntu 10.04, tried several other distros like Fedora, Mandriva, and several gnome or KDE variations of GUI's for each.
*Disclaimer*: I am extremely biased to Gnome, especially now with Gnome 3. Sorry KDE, I'm trying to get away from Windows & having to use my mouse so much, not use it to click different looking icons.