The rumor mill has been pointing to Apple exiting the Pro market sooner or later. I wouldn't be surprised to see another revision to the Mac Pro line but I've already decided on going with a Windows box for my next machine. The factors that led me to that conclusion include:

-OS X Lion
-Final Cut Pro X
-Woefully infrequent hardware revisions (see Macrumors buyers guide) and relative lack of options
-Price

That said, Apple is an easy out of box experience. I'm no longer willing to pay that premium though. Build 2x 12 core Windows machines for the price of 1x Mac Pro!