As a consultant, I face the occasional problem of having to work on source code that lives behind my clients' firewalls. Often, getting access to their VPN is difficult, like when the engagement is very short and the VPN red tape copious.
I've tried emailing zips, setting up a WebDAV share, and various other strategies, all of which had one shortcoming or other. The best solution is, of course, a source control system of some sort, but even that I've had problems with (e.g. the combination of the client's firewall and my ISP blocks the port(s) we need).
For a couple of weeks now, I've been trying a new strategy. Using FolderShare, we create a shared folder that we both have write access to. Then we turn it into a Bazaar repository. On each end, we pull from and push to this folder/repository, making it look a lot like a source control server. And so far, it works great. It even runs over HTTPS, which should make any suspicious sysadmins slightly happier.
I imagine one could do the same thing with CVS or Subversion , although I haven't tried it. Bazaar seemed like a reasonable choice for two reasons: a) it's more "folder-y" than most SCC systems, so it seemed like a natural fit, and b) Sam Ruby thinks it's cool, so I wanted to try it out. :)
 You might even be able to make it work with SourceSafe. But then you'd have to use SourceSafe, and why would you use something that's both worse and more expensive?