The Inq saw one of Intel's Tigertown based servers last week and says it's pretty fast:
Imagine a four way Woodcrest, and you have an idea of what you are in for. The interesting things are not in the macro structures, it simply looks like many other four ways, but in the details.
First, look at the north bridge on the mobo, it is huge and made of solid copper. Other than being a dead ringer for a landing pod from several anime series, it is meant to dissipate a good deal of heat. The chipset is basically Blackford extended to four ways. Blackford was about a 35W part, so if you extend it out to four FSBs, crank up the speed to switch between four of those, and possibly up the clock a little, you end up with a lot more than 35W.