FB-RAM has very high latency because of the buffering. However, to help compensate for that, Intel typically has a much better cache subsystem. It also runs very hot and uses a lot of energy compared to competing memory products. On the other hand it does allow for lots of banks of RAM which may be important if you need lots of RAM. I didn't look at the Dell specifications as to how many are allowed on this particular motherboard.
I would much prefer a dual-quad based on a C2Q over a Xeon, unless I needed an enormous quantity of RAM that FB-Ram can supply
I haven't worked on a significant number of Dell machines in the past year, so I can't really dispute Merc's issue with Dell's reliability.