How many people will upgrade?
The problem I'm starting to see (for Apple at least) is that the new iMacs are starting to look like awfully good alternatives to spending $3000+ for a Mac Pro tower.
The performance gap has been narrowing with new iMac refreshes and updates, while the Mac Pro has been completely stagnant.
I have a Mac Pro and one of the new 20" iMacs, and for most things I do, the speed difference is negligible, really. The Mac Pro can handle concurrent tasks without slowing down as much as the iMac. But in some situations, the iMac actually completes a given job FASTER than the Mac Pro does - when you're only running the one application on both machines.
Unless you spend most of your time in one of a few specialized "pro apps", or you tend to do a lot of background rendering/processing while expecting another app in the foreground to run as though nothing else was happening, the Mac Pro is hard to cost-justify right now. (Sure, I realize it has a bigger memory capacity, much more hard drive expandability, and you can pair it with whatever display(s) you like -- and it has the better video card options to make 3D gaming enjoyable. But ultimately, that amounts to paying a BIG premium for more slots and bays on the motherboard, you know?)
Blu-Ray included in some/all of the new Mac Pros is a good move for the future -- but it's strictly an "incremental change" in the grand scheme of things. The Mac Pro needs a new generation of motherboard/Xeon CPU inside it to be a "worthy upgrade", PLUS get some new video card offerings for the thing!
How many pro users will actually use the new MacPro systems?