These guys run huge networked Mac Pro setups in the studio and that's not going to be changing for the foreseeable.
One of them has had two motherboards fail on his out of warranty Mac Pro at home, and I believe they're called something fancy like Logic boards and are $1k a throw. He's also instability with whatever the latest OS is with random crashes. His is a totally dedicated DAW machine, with nothing weird on it at all. Interestingly he also has dual iPad touchscreens for DAW control, although I still prefer physical knobs and faders myself. It's possibly also worth noting that there are plenty of rumours that Apple will be ditching it's Mac Pro line in the not too distant future in favour of infinitely more profitable i products. Where that'll leave the professional community is anyone's guess.
I'm not knocking teh Macs at all, I plan on getting a hugely powerful 27" iMac soon which is plenty for running any kind of home DAW. I really have a Logic itch
