I agree iMac is tough to beat for the price. I would love a Mac Pro, but way too pricey. I am also leary of the new design.
I bought an iMac from the Apple refurb store, Quad core i5. I loaded it with 16gb of memory and it does a pretty good job.
I am sure a Mac pro would be much faster for rendering, but I set my iMac to work overnight. I have other Mac to use while my iMac chugs away.
I think people who dog Final Cut X and Logic Pro have invested a lot of time and money into other systems. But, I have yet to find anything I cannot accomplish with Final Cut, Logic and Compressor. I have never had crashing problems with any of them and the ability to use Qmaster to share the cpu load is pretty fantastic. I used a mac mini as a node and it worked pretty well. I don't know of any other software that can pull that off as well as Apple designed products. With the quad core iMac and Final Cut, I have yet to need this.