Nvidia has just announced it's Tesla Card, which uses it's GeForce 8-series GPU on a card with over a Gig of memory for use in number crunching applications. Since these cards are not tied to any video display output, they can be massively overclocked compared to their videocard cousins.
Pop a pair of these cards into your system, and you will have over 1 TeraFlop of computing power. To put that in prospective, IBM's Blue Gene is the world's fastest computer, at 360 TeraFlops. So that means that you could have the equivalent computing power of Blue Gene in you server room with only 180 computers with 4 Tesla cards in each of them. That is a doable for many companies and universities, or heck, even many collages. Of course, at that point, you are I/O bound, which is a problem with all supercomputers.
Still, having a Teraflop on your desktop is an ubercook geeky thing to have. All we need is a good real-time fractal program to play with...well, at least that is what I would want. :-)