My Linux box is at 73 days and counting... (would be more without power outages, thankfully I have a UPS now as of last boot)
As far as my desktop, not so great, I used to be an uptime whore, but I don't really care about it all that much anymore, and with my dual-booting between Windows XP and OS X (Yay Hackintosh) it doesn't tend to be that great anyway. Currently at just a day and a half. (Spend most of my time in OS X, but was in Windows gaming Friday night.)
Back when I was in a purely Windows world, my record was about 70 days until I got bored and rebooted.