One of the things that the Mac Mini is missing before it can be a full on HTPC crammed inside your entertainment center is support for Blu-ray. Apple has so far not seen fit to cram a Blu-ray drive into its offerings and the Mac OS still doesn't support Blu-ray playback natively.
Still, the upgrade kit from Amex Digital adds one of the biggest parts of the puzzle that is missing, the Blu-ray drive itself. You can use Boot Camp to use Windows for Blu-ray playback. The kit will surely break the warranty considering that you have to open your Mini up for install.
If you still want to give it a go, the kit sells for about $199 and while it can't burn Blu-ray media, it can burn DVD and CD discs. Isn't it about time that Apple included Blu-ray drives in their computers officially?