That's an excellent feature. the scenes in unity are binary and not merge-able. That feature alone left me considering other options when I was looking at game engines.
http://the-witness.net/news/2011/12/engine-tech-concurrent-w...
And they've also improved the merging story, see: http://blogs.unity3d.com/2015/02/17/production-workflow-impr...
Hopefully this was improved in Unity 5. One of the buried release notes mentions a new merge tool for scenes and prefabs in the engine.