If I may interject, distributed computing is used 24/7 by some very good projects. If you want to contribute to protein folding for medical research, or even help seti process their data, there are clients you can download. They allow you to donate spare CPU cycles.
I find the way the networked pcs were used to decipher code fascinating. I thought that only a bank of big bad supercomputers was used these days.
Can I volunteer my computer to work on some NSA activities? I would only be doing this strictly philandthropic task for the benefit of my country, of course. ;)