I switched from SETI a few weeks ago, because I just don't feel Seti is worthwhile. It is very unlikely to ever find anything. Then, RC5 doesn't have much of a purpose, but it will end eventually, so I can move on to other projects, which will, in turn, end. Seti just goes on forever and ever.
I'm contributing an athlon xp 1700 and a celeron 566, btw.