Seperate WP installations -> single 3.0 multiblog

Hi,
I run several different wordpress sites and read that there was new support for multiple blogs in wordpress itself.

Can someone kindly explain how this works, if it’s something where I can merge all my sites together easily or is it not what I think it is at all? Ideally, each site would still maintain it’s own appearance and layout and so forth. Is that the kind of thing 3.0 allows or do I still need full and seperate WP installations for them to be their own living, breathing entities?

Thanks.