As much as I'd love a Mac Pro, I'd rather spend that kind of money building a custom system capable of running whatever operations system I want. There's a device, EFIX, which plugs into your motherboard and emulates the EFI environment of a Mac (as opposed to BIOS on a PC). There are a few drawbacks: it's a couple hundred bucks, you're limited to using compatible hardware, and each operation system needs its own hard drive. Compare that to the benefits of being able to build a system that will run OSX, Windows and Linux natively, and the drawbacks don't look so bad. Even with the cost of the device itself, you can build a system pretty darn close to a Mac Pro, and still save a bundle. Even the hardware restrictions aren't all that restrictive, you just have to consult their site before buying anything.
Personally, my Macbook Pro does everything I need a computer to do at the moment. If anything I'd like a Mac Mini, to act as a server for my iTunes and such, so I don't have to keep the laptop hooked into workstation mode all the time.
That said, I do miss having a desktop to poke around in sometimes. The fan in particular gets annoying when I'm running a video game, rendering a scene, or encoding a video. Heck, watching a vid on YouTube or Vimeo often eats up so many compute cycles the fan kicks in.
Desktops might be going away for the public at large, but I think there will always be a place for them, in my life anyway.
