Just a quick post to mention that I've been successful lately running Mythbuntu on a Mac Mini Intel.
I'm actually driving my 1080p projector at full resolution via a DVI->HDMI cable, and utilizing the fiber-optic audio output (built into the normal audio jack) to output DTS/Dolby passthrough from MPlayer.
My Mac Mini is running a dual core 1.66mhz cpu, with 2gb of RAM.
Currently I am about 95% successful. The only content I have trouble with is direct ripped blu-ray content in MKV format with DTS audio. This plays somewhat choppy at 1080p. I am working on getting the CoreAVC codec working with mplayer to fix this problem. I'll be sure to make a post once I do.