These tools are really fantastic for collaboration. It’s great not to have to rely on e-mail attachments. However, I still have major concerns about privacy/security, especially where Google is concerned. I don’t know if e-mail is any more secure (–maybe I am just being paranoid), but Google doesn’t have a great reputation where privacy is concerned.
I’ve explored Google docs in the past, but I have not earnestly used any of those tools for my everyday work yet, partly because of privacy concerns, and because I get the impression many of the people with whom I collaborate are either reluctant to get Google accounts or to use these document features. Also, I think a lot of times it is habit to send e-mail and I sometimes forget that these tools are available.