For instance, to stay with the protein folding example, maybe bitcoin could have used an algorithm that used similar logic as the one used by the folding@home project but with different input data and expected results. Once the hardware is no longer needed for mining it can be easily repurposed for research.
It makes you wonder if we'll ever hear of anyone turning their bitcoin cluster to this purpose. Perhaps someone unauthorized.
Edit: Downthread, nwh explained why this isn't possible:
> No, they can't crack passwords. They increment a nonce at the end of a supplied string and only return if the nonce results in a low hash. They're not a generic "fast SHA" device like you're thinking.