If if the display port on the mini has multichannel audio enabled it would make a great HTPC.
That would be cool, but even just with TOSLINK it will be pretty darn good, unless you are on the bleeding edge of 7.1 audio processing, and have a brand new receiver than can pull the Audio out of the video cabling.
I would have my HT mac split anyway. The mac would sit with my audio components, and be cabled with optical to my receiver, and cabled separately for video.
FW800 is a nice touch, and will make it nice for use with a FW800 Drobo, or something. Unless one goes with a Network-Attached storage device.
I hope the case is easily accessed, with screws, rather than a putty-knife. The internal 2.5 can be changed out to a fast SSD to run the OS(s) and sharing, and off-load the main storage to external redundant backup, like a Drobo, or some other array, or a more centralized large-cap file-server via gigabit ethernet.
As long as this has the video horsepower to actually display HD-grade local video, and good-quality streaming video without major issues...
Something that I can hook an eyeTV tuner and video encoder, a Griffin RadioShark, and other HTPC type equipment to, and control with an IR remote, and bluetooth keyboard and mouse.
Oh, and to run another one as a dual-monitor workstation, and a third as a headless mini-server.