i have succefully installed LinuxMCE on my MacMini 1.66 Ghz / Intel Core Duo !
I will write a small howto, and post it here probably this weekend. ;-)
Everything seems to work fine. Except the Intel 945GM still have performance issues...
The fading of the background-images from flickr is not as smooth as i expected.
Anyway, LinuxMCE looks great.
We have just added an Qt based Orbiter (based on Touch Orbiter) to the svn and are testing it successfully on a Mac Mini and Ubuntu 10.10...and we will test it under Windows too soon (we dont expect any problems with this). Now this is an Orbiter and not a full MD so it has some limitations. But if you just want to have an Orbiter available to you on your Mac then this really works nicely (and it flies too).
All the best