I have been using git for source control with no issues (haven't tested in a team environment however).

Not sure if you were aware of this already but theres a non-default setting in the Unity preferences for enabling "Version control support" that basically makes Unity save metadata in a text format instead of its standard binary format: http://docs.unity3d.com/Documentation/Manual/ExternalVersion...

Personally I haven't had a problem using Git. I also haven't done that in a heavy team environment but I've heard good things in general since 3.0ish.

There are a couple things to be aware of regarding how you set up your .gitignore, and now, in 4.3, apparently meta files, but, it's pretty straight-forward, IMO.

I'd ask on the forums and get a current response... a lot of problems with the external VCS were things from back in 2.0ish land, which was quite awhile ago.

You really can't have multiple people working on the same prefabs or the same scene at once. The files are text, so you can merge them, but anything more than just minor changes will not work properly and someone will have to redo their work.

Working on code is fine and your normal guidelines apply to simultaneous work.

I have Unity projects with 3-5 teammates and we don't run into too many problems with scene/prefab merges. Normally each person is working on separate stuff so it would be rare for 2 people to need to touch the same prefab or scene.

If your scenes or prefabs are huge and it becomes a problem then you probably should think about redoing your architecture to keep your scenes and prefabs smaller.