Buying a Mac when it is this far through its product cycle is always a difficult decision, but you should just ask yourself; Do I need this much power, and do I need it right now? If yes and yes is the answer then buy it now. If you answer no to either then consider waiting a little while, or buy an iMac instead (they wont be significantly updated anytime soon).
I think we will see a Mac Pro with a Gainstown platform MB (dual socket) and Nehalem Xeon CPU's @ 2.93, 3.16 and 3.33 or more Ghz giving 8 CPU's and 16 threads. 3Gb DDR3 as standard (triple channel) with 6 Gb optional. 500Gb Hard drive standard. New Cinema displays.
I think we will see this available and shipping before the end of the year, but I dont want to give anything more definite than that.
So if you NEED a new Mac pro before christmas, dont wait.