If you have a whole house HDMI switch, you NEED the new Mini since otherwise, my switch doesn't work. Surprisingly, the new Mini is twice the framerate when doing Handbrake encodes of my old 2Ghz mini. Not sure why it gets twice, but, it does. This is a major difference for me. Encodes that took 2 days now take < 1. On the 2Ghz mini I had, if I was doing an encode and I wanted to watch a movie, it would stutter, so I had to pause my encodes. Not with the new mini.
I also have the ability to hook HDMI up as mentioned, AND, put optical out into my AV receiver. I can then play music through the receiver as well through the optical.
So, those were the major features of the new Mini for me. Definitely worth the $200+. I sold the old one on Ebay for $460.