Here's the thing: for my private development work (a.k.a. PHPExcel 8-)), I've been using Subversion as my source-control server (and client). As the PHPExcel is hosted on CodePlex, one would suspect I would be using the Team Foundation hosted service which is provided for free. Not really... Here's the thing: CodePlex provides a web interface to work items, which me and my project members use a lot. But since one needs Visual Studio to use the TFS code repository in a comfortable way, without having to use any command-line tools, I decided to use Subversion as the source repository.
Some cool news: the CodePlex people have released a TFS - SVN bridge, which is a man-in-the-middle proxy that translates (some) SVN command to TFS. This means anyone using SVN can now also use his (or her) tools to connect both to a Subversion server and a TFS server.
Update: I just spotted another TFS client written by Ben. It provides a lot of functionality similar to TortoiseSVN for Subversion, but does not use the proxy described above.