Wired had a nice article about the motivating power of statistics, and the positive sociological pressure that motives members from feeling they are part of a group. There's five excellent reasons to keep track of your workouts in this article.

Kde's Step is a good basic physics simulator. It is part of kde's education project.
From their description:
Step is an interactive physics simulator. It works like this: you place some bodies on the scene, add some forces such as gravity or springs, then click "Simulate" and Step shows you how your scene will evolve according to the laws of physics. You can change every property of bodies/forces in your experiment (even during simulation) and see how this will change the outcome of the experiment. With Step you can not only learn but feel how physics works !

There's a similar project out there called "Seventeen or Bust" whose goal is to find primes that will eventually prove a conjecture. To date they have eliminated 11 of the 17, leaving only 6 candidates left. I prefer to donate my cycles to them since there's bound to be a big party when the last candidate is eliminated and the goal is completed.