I was just looking at the NetBSD site today looking to see if they happened to have updated anything about the MacPPC project and happened to find a project that ported NetBSD to a Cobalt box. Now keep in mind this is only for the MIPS RaQ's.
Considering that we always talk about how Cobalt have their own version of Linux compiled for the hardware this would be a cool project. I hope that someday someone finds or releases a way to provide a upgrade path for the 3/4,etc... when Sun won't support the machines anymore.
http://netbsd.org/Ports/cobalt/