I currently own a Pi myself and run the following Pi OS's..
- Pidora
- Rasbian
- RISCOS
- Bodhi (they dropped the ARMHF project october last year so this is now obsolete)
- Slitaz
I think WattOS has a good market here.... considering the competition... Risc is not a linux os and has had to be heavily modified to work on the pi.. Slitaz is uber tiny like their normal linux os is. awesome os but complex to work with. Pidora... fedora never really got the job correct.. leaves good old Debian there with their rasbian.
You also have the old XBMC (classic!!!) , raspbmc and openelec
Only other linux os i know of on Pi but i dont use it.. is Arch Linux .. and also ladies and gents lol... Android ... yes Android!!!
so in a summary... there are only 3 official LINUX releases for the Pi
Rasbian , Pidora and ArchLinux (diy os)