As of December, I'm all Linux. I run Ubuntu at home. I use Linux at work, except when I need to debug OS-specific browsers. I never want to go back; Gnome hits my sweet spot. I want an OS that starts up and becomes invisible until shutdown, and I never want to touch the mouse. Ubuntu's out-of-the-box installation is probably still unusable for people without a tech background, but I love it.
I spend most of my time in Docs, GMail, Google Calendar, lots of Chrome tabs for testing + looking up reference material, Emacs, IntelliJ, and lots of terminals. I almost never need other software, and when I do, it's an apt-get away.
I've had challenges - I've never seen Ubuntu completely work on a fresh install. My wireless failed on my newest desktop install. The sound on the two before that. They never bundle my wireless driver, so I drag my desktop over to my modem. My printer gives baffling error messages. My old webcam arbitrarily rezoomed as it pleased. Gnome 3 overrode the "invert colors" keyboard shortcut, which I use heavily. I needed to steal time on my girlfriend's iMac to run Portal 2. My supercharged Toshiba laptop freezes when running on battery power (may not be Linux's fault).
But these are most of the problems I've faced in the past two years. I lose a few hours of productivity every few months in exchange for massive productivity gains while working.