Yeah I run an HD5850 and when I went looking for a second one to run in Crossfire I kept seeing all of these references to Bitcoin being the reason they were hard to find as people were scooping up all of the remaining stock.
The way I understand it is that you can generate them with a folding at home type of setup , but the folding serves no real purpose other than to generate this limited currency.... Right now a high end CPU takes about two years to finish the calculation , but video cards are much faster than the CPU's.
Those who got in at the beginning will have have the most bitcoin and the most value as it continues to be limited with no real method in place ( currently ) to generate more than a set number.
Kind of amazing for me to see the people generating their own electronic currency.