The iPad 2 just got released, is Unity already iPad 2 compatible or do we have to wait for yet another new release?
It should be compatible.
Anything that runs on the iPad 1 should work fine, as long as you take the more powerful CPU and GPU components into account. (I.e. make sure your application logic works independently of the frame rate. But you should be doing that already!)
As the iPad 2 runs on iOS 4.3 its to assume that it works fine.
To worry you normally only have on new iOS major versions.
Just keep in mind that unity is not multithreaded, so the second cpu core will only give you limited gain (stream in assets and audio primarily, but thats for some already a fair amount of gain naturally), but the GPU will surely make happy faces 