I use RamDisk 98 with win98se, in it I run seti, gamma, and the IE Netscape cache. I can't say what the performance difference is, as I haven't tried seti on my HD. It made a very small difference with gamma flux. Seti only hits the HD once every minute or two, so there's probly no real speed gain. I like RamDisk because I can now have the HD spin down with gamma or seti running, I have RamDisk set to backup every six hours, giving the drive a 6 hour rest. Putting the browser caches in there made a noticable difference in performance, and it doesn't hammer on your drive when surfing. I've read that RamDisk can sure speed up wav or graphix file editing, need lots of ram though.
Happy alien hunting!