I can't see myself switching from Win7 for at least another few years. My OEM copy of it cost me Â£80, so basically I'm paying, what, Â£20 a year for it? And frankly, given how well it works, I feel it's worth it.
I tried running Linux (Debian to be precise - Ubuntu, oddly enough, wouldn't work) on the same hardware and gave up. Windows Media Center alone is worth the price of admission, and before anyone says, MythTV is in no way, shape or form a good alternative - I know, I tried. The configuration headaches alone ruined that, and something like MythBuntu made no sense as this is a general purpose gaming/browsing/office work/whatever box which happens to sometimes moonlight as a media centre.
Meanwhile, my laptop had an interesting bug where whenever it went to sleep it would be 50/50 as to whether it would wake up again, and if it did the clock would suddenly be three days in the future. No such bug on Windows, on Linux it was crippling, as things would suddenly refuse to work, I'd look up at the clock and swear under my breath.
Â£20 a year for not having to deal with that crap strikes me as a good deal.