Usability, thy name is Ubuntu.
I'm sure if you're a geek you've heard of Ubuntu Linux. If you aren't a geek, hopefully some day you will hear about it. If you aren't a geek and continue reading this, well, that day will be today.
Ubuntu is so incredibly good that I find it hard to describe adequately. My last attempts at running Linux as my primary desktop OS included Fedora Core, SuSE, and Debian. They all pretty much suck at it, and suck pretty badly - it's possible to screw with Debian or Fedora to get it working well, but it's ultimately never worth it.
There's been this huge void that nobody could really fill, and I have to assume that's because coders typically value functionality much much more highly than usability.
But Ubuntu finally gets it right. You install it, and it works. Wireless, sound, bluetooth... it all works. A lot of the credit has to go to Gnome, which is finally getting good - but Ubuntu throws it all together in a great package that just gets everything right.
This is finally a Linux distribution I'd feel comfortable giving to my parents, but it's also one I enjoy using myself. There's a hell of a lot to be said for that.