Well, they report that the CPU is significantly beefed up, and the graphics have about ten times more power, and if you are doing VSTi on an iPad, you can't have TOO much power, and if you do any gaming or graphics intensive stuff (video editing?) you ought to see a significant improvement. If you aren't doing much but the internet and a .PDF viewer, perhaps an old one is fine.

The cameras are new, too. Personally, I think that it's enough to warrant a new one (going to get one in a few weeks, after I get my new iMac), but for users of the old one, perhaps not. Is saving a couple of hundred dollars worth losing all the new one does? Up to you, my friends...