The Mini is an awesome media center because:
*The form factor is perfect for TV use
*Supports DVI out of the box, HDMI with an adapter
*Includes all of OSX's basic a/v software tools like iPhoto, iDVD right out of the box
*OSX has a very nice STB-like interface if you use the remote
*It can act like a STB when you want one, and a computer when you don't.
The Mini has some limitations:
*Graphics power underwhealming, might be fixed if Apple doesn't kill the line. Then again, it might not.
*Gaming support is classic Mac- little to none.
*1080p video is a challenge for the unit, though 720p is fine.
*no integrated memory card reader. Apparently, apple is allergic to them.