Haiku shows a lot of promise despite how few developers they have. You should really give it a spin, especially when they hit beta.

If they finish their Wifi implementation (it works, even with WPA2 now, just doesn't have a complete GUI), bring their Webkit browser up-to-date, and get a bit more stability it would be a pleasant system to use on a day-to-day basis.

I honestly think if it had the momentum of a larger community, it could easily be open source's triumph on the desktop.