Macs and PC's use two completely different processors and they do not have a one for one equivalence, that is what the previous poster was talking about. As far as going "totally", Mac, the question that comes to mind is what programs are you running? If you are doing anything with media you're on the right platform as far as software is concerned. If you're a gamer the consensus on the boards is the only way to go is with a PC decked out to game with, or get a console. There are a ton of Apps for the Mac, Office, stats programs, mathematics programs, web browsers, etc. So the only thing that should keep you from switching over to the Mac completely is for software that just is not available for the Mac like AutoCAD, or ArcView. There are alturnatives to programs like AutoCAD such as VectorWorks, which is great.
I am not sure what you can expect from Apple in the near future as far as the iMac is concerned, personally I would wait until the next revision of the machine to see what is being offered.
As far as VPC is concerned, it runs OK, but it's not as good a real PC and never will be. If you need to run the occational PC program VPC is a must have and more than adequate. I run it on both of my machines, a 867QS and 1.25PB.
I say go Mac unless your need a PC only piece of software and cannot substitute it.