Just about all of your favorite major media outlets have a preview of the new 2008 Shimano Deore XT group set online right now. I believe Singletrack Magazine was the first to get its preview up, but Bike Magazine also has a good write-up.
To me, the XT group is the poor man's XTR. But ironically it usually is a better choice than XTR if weight is not your only criteria. The system is simply more durable. I'm of the mind that Shimano's XTR group really should be considered for the pros only that have a troop of people maintaining their bikes. They've got the money, time resources, and incentive to bend parts back in place or replace worn cogs after every hard race. If you take your riding seriously, but don't make a living from it, you are better off with XT.
Funny thing is that every few years it seems that Shimano releases the XT group with even better technology than it's flagship XTR group. I can remember reading a magazine's recommendation to go with XT way back in the 90's because of it's advances over the (then) current XTR, and this year may be no exception.
The most notable advance on the XT for '08 is the "Shimano Shadow" rear derailleur. Essentially the Shadow is a reduced profile derailleur that draws the hanging mechanism closer to the rear cogs and out of the way of danger. In fact, the entire derailleur is behind the quick release bolt so it is protected from damage if the bike crashes or is dropped on it's right side. (See the side by side profile comparison photo - notice the Shadow version is on the right).
Of course the group maintains many of the characteristics and options that Shimano brought to market with the 2007 XTR group. For more information I recommend the following from the GC archives:
