I echo the people in this thread that aren't surprised by the possibility that the Mac Pro's days are numbered, but I also echo the sentiment that...well...it sucks.
On the one hand, Apple has been grooming the iMac, particularly the 27" models, to do more of the work previously done by the Mac Pro. Toward this end, if you wanted a quad-core Mac, you've had the option of a 27" iMac for two years now. Previously those customers were Mac Pro customers; at the same cost with the inclusion of a 27" Apple display, those customers are now 27" iMac customers; no brainer. On the other hand, the 27" iMac has Apple's bizarre anorexia and is way thinner than any stationary "desktop" computer NEEDS to be. Given that:
On the other hand, the iMac is the single most user-unfriendly machine to service and/or swap components with. Couple that with the needlessly thin thermal envelope and the fact that, save for the video card and optical drive, the iMacs use all desktop components, you can't easily swap out your iMac's hard drive, and even if you could, you'd need a drive from Apple. The iMac, at its best, uses the best AMD Radeon GPU you can possibly get on a GAMING LAPTOP?! While the Mac Pro doesn't even employ the best video cards you can get on a desktop, they at least trump anything the iMac has ever had. I don't care how cool the iMacs are, until these two things are remedied, the iMac will never be a viable Mac Pro replacement.
The truly sad thing is that, with the current designs of the iMac and Mac mini being what they are, the Mac Pro is the best Mac desktop from both an internal design standpoint and a bang for buck standpoint. Once they kill that, then Apple has left their desktop segment with true crap. Then the options become crap, MacBook Pro, MacBook Air (which is also crap for the same reasons that the iMac and Mac mini are crap). So, MacBook Pro or...? Hackintosh? I'll definitely buy that Thunderbolt has potential, but what if I want a ton of internal storage? Oh wait, I guess with the Mac Pro gone, I HAVE to get a Hackintosh, unless I'm to switch to Windows or Linux. Awesome.
With Apple's notebook computers making up more and more of their Mac sales and their desktop computers making up less and less of it, it only makes sense that we will see their Mac desktop lines slowly die out. It's a shame that the first one to get the axe is the most useful one. Were it my call, I'd kill the freakin' iMac and never look back. My target thereafter being the Mac mini, which I would consider just as egregious if, it too, also had a glass panel that needed to be removed with suction cups or an exposed power supply that will shock the crap out of you if you are careless with it.