I think OpenDarwin looks to be an interesting project to watch. There are lots of areas in which to work, many loose or un[der]documented components, but a the same time, it’s pretty mature and robust. It’s not a pre-1.0 release.
It’s already platform agnostic, since it runs on x86 and PPC hardware. With the XPostFacto hacks, it will support PPC Macs dating back to 1995, so it’s not like you need a super modern box to get in and play.
And of course having Jordan Hubbard on the core team helps: interesting interview with him here.
It cleared up some of the vagueness about why Linux exploded instead of the BSDs. It’s not so much a quality issue, which is not to denigrate Linux — it did get to where it is today w/o the CSRG legacy to build on. It was a leadership void on the BSD front, versus Linus Torvalds’ well-documented blend of charm and laziness (lazy like a cat, I mean).
Perhaps we don’t really need another flavor of BSD (this makes five, I think) but a more accessible one is worth pursuing. And I think OpenDarwin aims for accessibility while still retaining high-performance and stability.