* First of One:

This true for HP workstations. Dell apparently managed to get SLI working
with the i5000x chipset, through a riser card that splits one PCIe x16 slot
into two PCIe x8 slots using a bridge chip. It's similar in principle to the
7950GX2 implementation, but uses discrete cards.

Right, but it uses an Nvidia brigde that basically makes something
similar like the 7950GX2. To the chipset this SLI setup looks like a
single PCIe x16 card, so it doesn't matter who made the chipset or which
chipset is used.

But that still leaves the i5000X chipset incapable of SLI.

Besides that, it's only certified to work with the Quadro cards sold by
Dell together with this Precision workstation, and only with certain
certified driver revisions (Quadro and Geforce driver are the same). It
might work with two 7800 or 7900 series cards, but I wouldn't bet on it
running reliable with other cards.

The chassis backplate is
custom to allow the slot brackets to line up. I guess Dell had sufficient
sale volume to justify this design with nVidia.

Well, Dell wanted to offer a fast workstation with SLI support. Until
the recent launch of AMDs Barcelona the current XEON 5100/5300 were just
kicking Opterons ass in two socket machines. Nvidia only has a chipset
for Opterons but not for XEONs, so the only way to get SLI on a XEON
system is via the Nvidia bridge.

But it's real-world value is very questionable. In the professional
market SLI is much more a niche than in the gaming market, and it's use
for professional applications is *very* limited. Besides that, it's
doubtful that it will be supported in upcoming driver releases. That's
probably why only Dell offers this option while the other big
workstation brand names (HP, IBM, FSC) are staying away from it.

Benjamin