Earlier quoted context omitted.
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.
I am legitimately surprised they're using a binary format for scenes. That is very anti-source control in general. The only binary blobs in the entire project should be assets (e.g. textures, sounds, etc). Everyone loves to whine about XMl, but I'd happily take XML for scene layout over a binary blob.
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.