I mean, I hate to really even bring this into the picture. But it's been a long-ass while since the MAC PRO line has seen a refresh... the last update was to the Harpertown architecture, and that was almost a year ago, or February rather as I recall. THe update was to 8-Core 2.8GHz, 3.0GHz, and 3.2GHz Xeon machines. Newer processors (ahem, Nehalem / Core i7) have come along and it's time for a major update.
People think that Apple sells few, and people buy few of the Mac Pro lineup, and that the demand is low, and this is not one of their flagship products. Rather, begging to differ, I think this is their bread and butter with their pro lineup that can run Leopard and pro apps, they need to keep the lineup refreshed. It's been too long, it's time for an update. Note: We have brand new iMacs, and the Penryn MacBook Pros, but the Mac Pros haven't been updated in quite a while.
Correction...the Mac Pro was updated in January a week before MWSF. Also, the update previous to that was a year! Therefore, the next update for the Mac Pro is very likely to be January 2009.