It's also nice to use a finely crafted piece of software that doesn't feel like it has been bolted together haphazardly (like your typical Linux distro).
That said, OpenBSD is probably the most organized project out of all open source projects close to the same size and scope. They release like clockwork, they do not (or try not to) rush new features out just so they can make the next release, and there really is an uncompromising drive for perfection.
I would love to contribute code to the project, but I have to be honest: though I'm by no means a slouch programmer, those guys seriously outclass me, and I'd be completely out-of-my-league.
Having perused bits of Linux source from time to time, I don't feel that's so much the case outside of OpenBSD.