I've tried this in CentOS 5.6 and Debian 6.02, both guests running under VirtualBox 4.04, and it works in both.

If you type `cd //`, it takes you to root like normal, but the pwd is `//`. Other than that, everything is like a regular root. You can traverse the filesystem like normal, but as long as all the paths you enter are relative, the double `//` will remain. What's going on here?