I totally agree. Should have 6 slots for the 4 core and 12 for the 8 core. IIRC one of the chipsets for the 5500 series Xeons can handle up to 18 slots so Apple really shot itself in the foot.
I'd really like to see an i7 based mid range desktop mac sitting between the iMac and the Mac Pro. They'd sell loads of the things I reckon.

One magazine did a head-to-head of the new Xeon workstations. I think they had a Dell or HP with 128GB of RAM!

Interestingly, to keep the performance as equal as possible, they usually shrink the main partition of the hard drive down to 60GB... They couldn't! Windows needed 128GB for the swap file!

I'd have a couple.

This bit I’m not following. I have 8 slots for RAM on my Mac Pro (two sets of 4 slots). I have to put RAM in pairs and balance the load.

Paul, the new processors support triple channel RAM so you need to install it in sets of 3 sticks per processor to get max performance.
4 sticks puts it back into single channel mode

If only it were so simple.

As saspro says the new Xeons use tripple channel RAM (in common with the Core i7 range which uses the same Nehalim (excuse the spelling) architecture.
In the case of the Mac Pro with 4 or 8 RAM slots (as opposed to just 3, 6, or 12) when you add a RAM stick to 4th (or 4th & 8th) slot it is still using tripple channel RAM but now two memory sticks are sharing one of the channels so the system actually slows down overall if you max out the RAM slots.
The best configurations for the Mac Pro are all multiples of three despite what Apple would like people to believe.

Things are further complicated by the fact that each processor requires its own dedicated bank of memory which is why the 8 core machine has 8 slots while the 4 core one has 4 (and why the 8 core has 6GB of RAM in its base configuration while the 4 core one gets 3GB). SO if you want to upgrade the 8 core Mac Pro you have to remove all 6 sticks of RAM and replace them with higher capacity RAM (expensive).
Apple did give the 8 core xServe 12 RAM slots so they obviously know that they stuffed up with the Mac Pro.

Rather than go for the i7 Mac Pro, I would prefer the previous dual-cpu model - it is slower and uses FB-DIMMS, but it was far cheaper and fast enough.

I tend to agree with you Gav.

The new Mac Pro seems to have some very silly design compromises... That said, so do many of the cheaper Core i7 and Nehalem Xeon based machines. It isn't until you buy a pro workstation model from the big names that the motherboards are really designed from the ground up for the new chips...