The Mac media center 0.1 alpha is now available. I'm sure it has its share of first release bugs, but that's typical.
Known bugs: "Garbage appears on menu screen on high (>1024x768) resolutions
TV output of mac minis can exhibit weird artifacts
Sometimes crashes at launch (1 in 10 launches)"
I have no use for this right now as I'm using XBMC on my Xbox to run on the projector, but those with Macs as their input may want to check this out.