I know an ISP which has several hundred SuperMicro servers - you don't buy that many if they are rubbish...
They definitely look like rebranded Supermicro servers from the details on the website.
There's plenty of good products from the big server vendors (HP, Dell, IBM and my current fave - Sun) so I would need a very strong reason to look at anything else. If you negotiate and pitch them against one another, you can get some VERY good pricing
They're very cheap. Which is fine if you can deal with the downtime. They also don't benchmark terribly well or look great in terms of power consumption compared to the big name brands.
On top of all that, if I have a failed anything in an HP server I know I'll have a replacement fitted within 4 hours, can't guarantee anything like that with the small vendors...
Boston's choice of components pays off in the power stakes, as our inline meter measured it drawing 22W when powered down and 182W with Windows Server 2008 in idle. With SiSoft Sandra pummelling all eight cores at 100% utilisation, this rose to a peak of 250W. The similarly equipped HP ProLiant DL360 G5 was measured at 30W when powered off, 213W with the OS in idle, and 310W under heavy load.