I'll go against the trend and argue that it can prove useful in certain cases.
While I fully agree that Dropbox is in no way a substitute for a proper VCS, it can come in handy when it comes to sharing binary files with others on the team.
The most obvious case is images. The guys whose task is to come up with several different designs for, say, a button on a webapp, will want to share a few psd files, which will then be reviewed by the one who's going to make the call.
Now, while committing assets such as images to source control is definitely worthwhile, throwing in all the intermediate versions isn't going to buy you anything, all the while making your repository bloated (which is especially true if you're using a DVCS). Nevertheless, Dropbox having some sort of rudimentary source control capability, you can still see the history of a file.
So yeah, I think that Dropbox (or Google Drive or whatever) can find its place in a team.