Fortunately, you can put that idle computing power to world-bettering use. Distributed computing allows a project like protein folding to be done across multiple computers simultaneously. The project is divided into pieces, and the pieces are sent out to computers with a distributed-computing client like BOINC. These computers do the work on their own, and when they're done, they send the results back to the project in exchange for a new piece. Countless science projects use BOINC to increase the speed of their calculations, including Folding@home, SETI@home, Collatz Conjecture, and Orbit@home. My favorite project, though, is the World Community Grid, which brings together multiple projects aimed at ensuring clean water, fighting malaria, and curing AIDS. As of August 2, my computer has done over four days of work for the Grid, returning 21 results and earning me 14,184 points over a month and a half.
Nearly all distributed-computing projects can be run through the BOINC client. Nearly. The very important Folding@home, which complements the work of Rosetta@home, has been around since before IBM started BOINC, so it uses its own client. (It also comes pre-installed with your Playstation 3.) You can run both clients at the same time on your computer, of course, as long as you have the power. Even if your computer isn't the fastest out there, you still have some power, though, to help change the world for the better, so why not?
Note: I found out about all this through Dinosaur Comics (link at the bottom of the page).