nuthin - 6:11 am on Oct 20, 2010 (gmt 0)
Seeing missing cache's today on sites that have obtained fresh links from sites that are frequently crawled. In theory; the site should be updated with it's new cached version after 48 hours (normally this happens).
This particular site has been waiting 1+ week.
Maybe Google's not updating these sort of sites at this minute... but no reason explains the dropping of the cached version.