Driver, Peripheral support
I think Linux is the best environment for working (I'm an embedded software developer), however I use windows at home, after using Ubuntu for three years. The reason I'm doing this is I bought an HP laptop, and use it connected with a dockstation, connected to a monitor, and use it as a DVD player connected via HDMI to an LCD TV. Not really a complicated setup.
Without turning the computer off, I can connect and disconnect from any TV/monitor and Windows will work just fine, remembering all settings I did before for all the outputs. Playing DVDs is easy with Media Center.
With Linux, getting the computer to do Dual-monitors is a pain, and disconnecting the monitor and plugging the TV screws it all up. I'm not saying that it's Linux/Ubuntu's fault, but until they work closely to ATi/NVIDIA and do some serious work, using it is a no-go for me, as I'm not up to edit conf files every time I want to play a DVD. Not to mention all the hassle with codecs/dvd playback encryption libraries, etc. So yes, Windows just works at many tasks, for whatever reason, and frankly when I'm at home that's all I want because I don't have the time to lookup in forums on how to do all these things. I'm really happy hacking all day long in a shell at work, but at home I just want to sit back and relax.