Heh, the X38 will have DDR3 only unlike the P35 and also have 2 PCI x16 slots which reduces the number of additional PCI slots (unlike the P35 with one x16 and one x4).
At least that's what I got from the Bearlake descriptions at the wikipedia entry.
It's funny how they describe the P35 as a low end chipset. That's what caught my eye with the X38.
And whilst this is a toms hardware forum, i saw a very nice comparison of the Crossfire running on the 975 chipset to running on the P35 on a rival site. Very interesting reading and quite pertinent to my iminent purchase of a new Crossfire PC.