I've been holding off an iMac purchase to wait for the 2012 model, and my main use for this machine is photo editing.
The decision for me is mostly easy, max out the processor and graphics card (I will be doing a little more video than I have previously done, now I'll have a system that can do it properly) and I've just ordered 32gb RAM from Crucial.
The only sticking point for me is the hard drive. I don't think the way Fusion works will be of use for photographers with huge libraries, especially if you access files randomly from the archive (if you only open them once to edit, Fusion won't think of it as a frequently accessed file, so it won't be moved to the SSD, if my thinking is right?.
So I'm a little worried there will be a bottleneck in speeds. I read an early report that briefly touched on this, I'll have to try and find it again.
That SSD only option is sooo expensive though