I don't know about this version, but keepassx creates a file in the same directory where the password kdb file is, and use it as a lock. But, keep in mind that

I don't know about this version, but keepassx creates a file in the same directory where the password kdb file is, and use it as a lock. But, keep in mind that dropbox can delay updates to the server (could be hours if you are disconnected) with no warning to the user, which means that two different users could update the same file independently and create a conflict. For this reason, it isn't suitable as an enterprise solution. Having said that I recommend dropbox as a poor man escrow, so that somebody you trust as easy access to all your passwords for banking, social network (keep your alt accounts somewhere else :-) ), servers' root, etc...