I had two gripes about the mini mac as the Projector Computer (obviously that wasn't enough to not order it).
1) Lack of gigabit ethernet. With a small laptop drive inside it'd be nice to have as much bandwidth out as possible. Someone suggested that maybe I could get a couple hundred megabits out of the firewire with some sort of ethernet to firewire adapter. I haven't found that, but I remembered that there's "IP over Firewire" in OS X. With a firewire repeater it can go over fiber and thus have Really Long cables.
Of course the repeaters are insanely expensive, so getting the Mac to stream DVDs from the linux box with 100Mbit ethernet is really a much better option. :-) Maybe it'll be fast enough over NFS? Otherwise external firewire drives will work.
2) No optical audio output for surround sound. That turns out to not be an issue at all. Tim Bunce (Tim, you really need to get a website!) pointed out that there are lots of USB sound devices. Yay. Hopefully that'll work. (Of course I don't have speakers and so on for surround sound, but some day...)
One more potential issue actually: There's only one monitor output. The "monitor" (Infocus 4805) is perfect resolution for 16:9 anamorphic DVDs, but painfully low as a computer screen. With DVI it's Beautiful. It can run in some odd squeezed 1000×600ish resolution too, hopefully that'll be enough to access all the configuration we need.
For the remote control we can use bluetooth keyboard and mouse and/or cell phones with Salling Clicker. (We both have T-Mobile phones and they barely barely work at home so at least we can get some use out of them that way ;-) )