tedster - 11:38 pm on Oct 10, 2009 (gmt 0) I can't say for sure, but I assume they do.
It's easier to find malware, I think, than it is to find parasite hosted content and links that are used to boost a real offering. Even so, Google does find that junk after a while.
There are certainly publicly available lists of open proxies and zombie machines - does google use these in any form?
I can't say for sure, but I assume they do.