This is very interesting. Also Primecoin seems to be helpful in the prime numbers field.
https://en.wikipedia.org/wiki/Primecoin
https://en.wikipedia.org/wiki/Primecoin
I'm more sympathetic to using big amount of calculation to actually doing something useful, like calculating prime sequences.
I wonder what other kind of (useful) work could be used as payloads for virtual currencies
Edit: This is perfectly relevant to topic of discussion and informative. BOINC is a completely valid platform for distributed computing for many different areas of research including mathematics, medicine, molecular biology, climatology, environmental science, and astrophysics.