I doubt the weak link is often the actual administrator in charge of virtual security..
Surely not, but the fact that Google is now hosting business services, they are quickly becoming the information sink of the universe. They have a history of easily folding to law enforcement, which makes me uneasy about hosting corporate stuff online. I just don't like all the big brother business, and while I use GMail for personal stuff, I wouldn't start trusting Google with sensitive documents, memos etc.
Web based tools have another huge problem. You're at Google's mercy for upgrades, feature changes etc. Does anyone remember the crap they started with the iGoogle sidebar? That sort of stuff quickly discourages corporate clients.