A company called Readify have come up with a hosted solution for Team Foundation Server (is this Sourcecode-as-a-Service? Sorry, lame joke).
I think this was a logical space for someone to move into given Team Foundation Server's abilities, web service interfaces etc. and one thing I really like about this idea is the ability to trial TFS easily before deciding to adopt it (either via an internal system or the hosted route).
From a purely technical perspective it's a nice validation of things like TFS scalability / support for geographically distributed teams and performance : just think Get Latest Version - I'm not sure a hosted sourcesafe solution would have done it for me :-)