What is multisite actually?

I heard that in wp 3.0 you have wp ù built in. Now I have a few questions concerning this.
I moderate different gaming blogs, all functioning thanks to wordpress 2.9 . HOWEVER.
If wordpress 3.0 offers multisite and I will be able to manage all websites through one backend, it’d be awesome.

Would WPμ mean that I can put all my blogs in the menu bar, and have the mmain website displaying posts etc from these other blogs.

Is this possible with wp μ or does it offer solely one backend for multiple blogs