Four Years of Mersenne Prime Searching

Hmmm...  it's been four years of running GIMPS (Great Internet Mersenne Prime Search) software on my machines and in that time I've checked 117 exponents and the project has found 2 Mersenne prime numbers (prime numbers of the form 2^P - 1)

I still think projects like these are a good use of spare cycles.  What distributed computing software do you run?