[asid61]

We use it with Solidworks after trying Dropbox and SVN in years past. It is absolutely amazing; making conflicted copies is nigh on impossible, and anybody can be taught to use it in a matter of minutes. Plus, the online repository and sharing is good too, with its integrated CAD viewer.
It has very few features, making is easy to learn with, but it also can't do things like locking assemblies and the like. However the version control is great.
The infinite file storage really sold it for me. We can store other stuff right along with just CAD files, like info PDFs about the files and renders.

EDIT: The SW plugin crashed some stuff for us when we started using it late last year. They may have fixed it by now.