I've been running Arsgeek.com on WP for a while now. I'm trying to get the wp-supercache plugin to work with my blog as I'm getting lots of traffic and this seems to be the way to go.
EDIT: Forgot to say I'm on WP 2.5.1.
In doing this, I noted that the plugin likes pretty permalinks - so I try to change my permalinks to this structure:
And when I do - my cpu usage goes from about 7% to 99.9% and stays there.
If I put it back to default (where a post looks like this: http://www.arsgeek.com/?p=1234567) it drops right back down to normal.