remote options for media centre
Remote control options are the Keyspan thingie or the "Salling Clicker". Take a look at it on VersionTracker. It is a bit of software that is pushed onto your Sony-Ericsson Bluetooth phone and allows iTunes, Keynote, Powerpoint, iPhoto, DVD-player control and even an etch-a-sketch style control of the mouse amongst a few other things. In iTunes, it sends the playlists to your phone and lets you browse the library, fast-forward, rewind, etc... All from your phone. I don't know what other phones it supports, but it works like a champ on my T68i and my friend's P900. It is possible to develop other controlly-bits on your own and many people have contributed. My personal opinion is that a bluetooth remote is more "elegant" as more of it is hidden. The remote control interface can essentially just map remote key-presses to apple-script commands. Most good apps are fully scriptable.
As the front-end to the media centre, look at MythTV. The Myth Front End runs on OSX today, although the backend is Linux only for now. Work that would be needed would be to have it launch the underlying iApps. I don't know what to do about DVD-ripping. Perhaps a wrapper to Handbrake. the advantage of using MythTV as the front end would be using other peoples' skins without having to do too much work. MythTV is a gnarly beast to master but probably a good long-term bet, from the interoperability viewpoint.
Essential options for the media-centre mini are the 512MB RAM option and the internal bluetooth module. The wireless is nice to have, but running cat5 along with the wires to the TV display can be done discretely enough and saves a bit of cash. Not to mention gives you better conneectivity. Full-duplex 100mbps is *much* faster than half-duplex, shared bus 54mbps.
Once I get my grubby little paws on my mini, it will be mounted vertically on my wall, next to my 30" lcd tv. I wonder how hard it will be to rotate the white plastic "top" with the apple logo on it 90 degrees so that when on the wall, the dvd-slot will be on the side and the apple logo will be right side up. I am sure that this is warranty-voiding, but aesthetics has its price...