I just found something interesting. when searching for information on google, I noticed that co-op (http://www.digitalpoint.com/tools/ad-network/) has a rank of 0 on google tool bar. All other tools from digitalpoint have a PR of 4 or more. it's not showing on google: http://www.google.com/search?hl=en&lr=&q=http://www.digitalpoint.com/tools/ad-network Link-vault.com is not on google either: http://www.google.com/search?hl=en&lr=&q=link-vault.com Are these tools being penalized by google?
Golly, as if Google has nothing better to do... I say it is a temporary glitch that has no meaning - just coincidentally you noticed this the same time 50% of website owners are finding that their sites have been de-indexed in Google.