Over 527 units I've managed to get my average time down to 3hr 33min 58.7sec. I think its still dropped, but at a very small rate.
At the moment I'm using the cmd line with SETI Driver on my home 2.53Ghz P4 and my work 2.4Ghz P4.
I know everyone mentions it here but if you can use the cmd line over the screensaver it really does produce a increase.