Best thing to do is go to an Apple Store and check one out. I actually was wondering the same thing, so I might head on over to my local Apple Store today and download the Logic Express Trial. My guess is about the same performance as a PowerBook, but the slower 4200 rpm drive might pose a problem.
If you're going to get a new Mac for a studio, and you're short on money, I'd get a cheap Mac Mini and a 20" Alu Display. Then, in a year or two, get one of the last PPC PowerMacs to last you a while. The reason not to go with Intel is obvious -- for the first year or so audio companies will be having driver issues and whatnot with the new platform.
Of course, the best thing to do is get a DP G5 PowerMac right now, so that it'll last you well through the Intel transition.