I heard a theory on one of the boards, and I don't know if this has been discussed yet, that talks about sites created after late 2003 are re-sandboxed for the more popular search terms. I launched my main domain in June of 2004 and my site has been hit hard despite the fact that Google assures me that I have not been penalized. Maybe all of us who are affected can include the launch date of our sites that have been "sandboxed" and we can see if there is a common theme? I am hoping there isn't because I was banking on the 2nd and 3rd phases of this update to fix my site. You'll have to use the whois.sc creationDate to be accurate.