http://www.filecloud.com/tutorials/desktop_xp.php
On the face of it, it appears to be just a way to map storage space on filecloud's servers to ones' machine in a way similar as one would map a drive letter to a folder or network connection.
Myself, I'm not at all enthusiastic about implementing that concept. Might be ok for others, but I prefer not to think of filecloud as a component of my system. It may be an innocent convenience for some users, but for me, if I feel the need too use a storage host, I'd prefer to do it at arms length(ala theirs' is theirs' and mine is mine). Just feels like they're trying to develop to cozy a relationship.