I don't really do anything aside from gaming that requires massive amounts of computing power. Certainly nothing that would require the services of a supercomputer. However, if I were one day to find myself in need of such a system I would likely attempt to build one, rather than drop the fat cash generally associated with supercomputers. That's exactly what one guy did, and he did it for dirt cheap.
I know that plenty of people will look at $1,256 and think that isn't a budget computer. They'd be right too, but this is a budget supercomputer, and that's about as cheap as they get. The system dubbed Microwulf is a Beowulf cluster that runs at 26.25 Gigaflops. That probably won't mean much to the average user, but that's just crazy in terms of price/performance ratio.
Here's a little food for thought. Sun's Sparc Enterprice M9000 supercomputer will cost you around $511,385 and will produce 1.03 Teraflops. While that's a lot more power than the tiny Microwulf, let's break it down in terms of cost. You'll pay around $496 per Gigaflop for Sun's machine, you'll only pay about $48 per Gigaflop. Damn, that's some cheap computing!
If you are interested in building your own pint-sized supercomputer, check out this awesome writeup of the Microwulf over at Cluster Monkey.