If you don’t mind your Mac Mini being slightly less “mini,” a big performance and storage upgrade can be gained by connecting a faster 3.5″ SATA drive. Unfortunately, there are two big difficulties, namely: 1) there is no external SATA connector on the Mac Mini and 2) any upgrade has got to be in keeping with the machine’s small form factor and slick looks. This particular hack addresses both issues.
Basically, I hacked up a NewerTech MiniStack enclosure to hold a 250gb SATA drive, which is connected directly to the internal SATA connector in the Mac Mini.
The author was kind enough to document two versions of his setup, a warranty friendly version that requires no serious modifications to your Mini, and a warranty voider version that requires a little dremel work to mount the eSATA connector flush with the Mini’s case.