I just finished deploying our local intranet set, and the management liked it so much they want to duplicate and create at least four additional sites for each department.
I was comparing and contrasting the different ways to accomplish this. Each site will be fairly similar in functionality and most likely share the same content types, with the possibility that there may be some tweaks added or removed. It will all mostly be the same though. As it is now, I am the only person who will maintain and manage these sites.
I could just copy my original, make four new databases and operate each one as a separate entity. That seems like it could become a management nightmare.
I also did some reading up on multi-site, which might be a better way to go. Since they will each share the same codebase, and this might make updates much easier, I am leaning towards this.
Then I researched Aegir. I am a little confused as to what exactly it might do. From what I have gathered, it seems to be kind of your own "webenabled" type of managing system where you can deploy instant drupal installs and still manage them from one control panel.
Does anyone else have any experience using Aegir? Am I on the right track? Are there any other alternatives?
I want to future proof this as much as possible and also make it as easy as I can on myself obviously.

Comments
I've been researching this as well
I think one big question (at least it was for me) is how are you going to handle accounts on these sites? I don't want to administer several sites user accounts and I didn't want to have to maintain multiple code bases so a mutli-site setup with a shared user database was the way to go.
You mention that a lot of the content types would be the same or very similar, but different depts would have different content. You may want to consider using a single site install and organic groups to separate the departments. You could also use something like the subdomain module to have sub-domains for each organic group.
Gil Creque
Interesting Gil. I hadn't
Interesting Gil. I hadn't considered organic groups. That would be great to hand off some of the administrative tasks to someone else to manage the users and other things. I could still manage the content from one central location as well. There would probably be at least 300 users total, with varying roles.