There are some discussions about the supported OS's in the Raspberry Pi Forums. And this is what is still holding me back from dancing and screaming about this project.
This is something I need to look into. I'll be buying one B when they are available anyway, but may get more depending on a few things including the OS question. The claimed "can play 1080p h264 video at 30fps" claim is most interesting to me, but if I slap Debian on there (which seems to be the suggested distro) will it be able to use that hardware video acceleration out of the box or will I need to jump through a few nasty hoops to get some proprietary chipset driver to cooperate?