Years ago, I tried SETI@home. I've been a space nut for ages, support SETI and the Planetary Society, etc. But it dragged down the performance of my machine back then (a Mac 6100, IIRC), so I abandoned the effort.
Recently, I got back into the fray, this time on a spiffy MacBook Pro, under Leopard.
Alas, I've discovered that it seems to interfere with sleep and the laptop now runs extremely hot and the fan even comes on (which it never did before). This happened over several days. I was initially head scratching as to what was going on, but then realized it must be the BOINC manager!
I'm now being forced to abandon the program again! This is a disappointment as I really wanted to help the effort.