I use linux only, and have done so for about 12 months. I've built up my "server" (also linux) to provide services including jabber, xoops portal on apache, email, ftp, shell accounts, quake 2, and most imortantly remote X sessions with all the nice C/perl/python/mysql tools my windows-using friends who need to do their Uni assignments.
Linux takes a lot of time to get it running nicely. You have to want to make it do things for you, because it sure 'aint going to do it for you. The reward: it's user friendly for my users, because they don't have to be their own sysadmin. They say "I want to be able to do this", or "I want my account to do this" (thank goodness for usermin!) and I can show them how to do it in 30 seconds (I've done it before) or I go away and install/configure some package for them (thank goodness for apt-get and webmin
Bottom line: I don't have any windows installation on either of my two machines, because I don't play games and I find Windows to be FAR LESS "developer friendly" than Linux. And as far as user friendly goes... as long as the user doesn't have to be their own sysadmin, it's pretty much the same as windows, plus they have, in my opinion, far superior developer tools at their disposal.
My 2 cents..
- Paul