I've been using Ubuntu on my main desktop for over a year now. A few months ago my girlfriend noticed the lack of error messages on my screen compared to hers (XP) so she asked if I'd install it for her. I handed her the CD and a beer and 30 mins later she was sitting in Ubuntu.

After an hour the screen went black. Reboot. Black screen. Kept doing this and after some fact finding it looked like it was choking on her crappy ATI video card. We went out and abought a $30 card with an Nvidia chipset and it's been running great ever since.

Moral of the story. While Ubuntu has very robust hardware support, your system might have something that it doesn't like. I got lucky. She was semi-lucky as it only cost $30 to get up and running. But it's been great ever since. I threw Ubuntu on my eeePC and it's been running great. Between the eeePC, her PC, my PC, and my 770, it's a linux house.

Weird that stuff just works now. (Not to say you'll never have any Linux horror stories, but overall a way better experience.)