FreeBSD is really nice - OSX is actually using a FreeBSD userspace. I actualy prefer FreeBSD to various Linux distros because I feel the design is much more logical and there isn't a ton of custom/non-conventional abstraction layers sitting on top. The downside is that desktop hardware support is nowhere near as good as Linux - but as a server OS it is wonderful. I am using FreeBSD as the base for a little project of mine and find it incredibly easy to work with.
Chromium OS is all based atop the Chromium browser which, alas, will not run on PowerPC (and it's unlikely we'll see it running any time soon). The reason being the V8 JavaScript engine contains an awful lot of x86 optimizations to make it faster, which makes the task of porting it to PowerPC a lot more difficult.