I just updated my Macbook Pro to Snow Leopard (10.6.3) from Tiger 10.4.11. My activity monitor was showing 55% cpu usage but no process that was taking the resources. This was incredibly annoying and led me to work the last hour trying to figure it out. I uninstalled a lot of crap, moved preferences around, deleted user data. It turns out I needed Rosetta (which wasn't installed?) and it was cause by my Epson V750 scanner (Epson Scanner Monitor). I downloaded the latest SN compatible drivers - which triggered the Rosetta install. Immediately the CPU dropped and I am sitting pretty once more. I'm putting this in the blog so that someone doing a search for phantom CPU usage OSX or high usage fans at 100% OSX Snow Leopard can find the problem and a potential solution.

This is Jon. My friend in the Mac lifestyle. Both of us avoiding computers in a quant little house in Maine. Our wives are somewhere... just taking in the sun. I'm ready for another Maine vacation I think.