We have used Dell for all the standard workstations for about eight years now, and the chassis and boards in the previous generation T-series are excellent. Quiet, robust, loads of expansion, great cooling and easy to service.
My only complaints have been that Dell don't use standard ATX-sized PSU's and we've had a higher-than usual return rate for our PSU's - possibly because we bought 35 in one go and there was a bad batch. Dell have been great about replacing them - They even shipped me a couple of extras so that I could just swap out a dud immediately rather than wait around for the next-day support window.
We only have a small number of dual-socket Precisions, but they're T5400's and look similar to the T7500 you're looking at. Processors and RAM are cooled by ducting from 120mm Delta-brand ball-bearing fans through some pretty serious heatpipe-towers and these things are very firmly mounted. I genuinely think it would be hard to build a homebrew dual-socket machine that ran as quietly as the Precision workstations. The only drawback is that there are no fan filters anywhere. You need to keep them clean, since the front grilles can get truly caked in dust.
Oh, and given how big they are, I expected more disk bays. I guess that's the price you pay for getting a machine with an E-ATX board in it....