We’ve moved our sources in VSO and so far everything is good. After installing Team Explorer 2013 with Update 2 on our Teamcity build agent, we’re able to run automatic builds and the automated tests, as well (ours are XUnit-based and while Teamcity does not support them OOB, the configuration procedure is easy and well documented on many blogs).
Now, here is why I’m writing this post: only the sources for one project are in VSO, there are many other projects I’m responsible for and their repositories are still in the on-premises TFS.
I really like the way VS allows the user to switch between TFS servers. It Just Works! We’ve been working like this for some time now and no problems occurred! You can work with VSO, then switch to another TFS server, open another VS instance and connect to a different TFS server … and it works, no login failures, no poorly synchronized repositories, no bad CI-s.