Finally making the jump to Lion Server on my old machine, after deciding that XBMC is a decent enough replacement for Front Row. Plex lost me when they tried to tie everything to a "myPlex" account (literally, the software wouldn't work unless you signed up – #plexfail).
* Media Center that works with Apple Remote and plays all my media
* The ability to host a shared USB drive that supports Time Machine over wifi
* Support for an AirVideo server to stream to my iOS devices
* DNS server for local internal network
* The ability share a printer on the network
Doing the install on an external USB drive first, and if that works out well, I'll do a clean install on the internal machine drives.