At MWNY I saw a rep run an OS X-native version of the 2.66 seti beta. I think maybe it's carbonized instead of cocoaized, but it's just a guess since it looks exactly like the current mac version. So it sounds like an OS X version should be out as soon as the 3.0 client is released, which shouldn't be too long as the 2.74 beta seems stable.
As soon as my beta comes (still Being Assembled!) I'll be installing the rhapsody-5.6 version, the one that's seti 2.4. It should be quite a bit faster than the 3.0 version since it doesn't have all the science, not to mention the gui. Science is good, though, I suppose...

Maybe the seti people should just give a 2 WU credit for every one done in the 3.0 client. That would make everyone switch!