I've installed Drupal in various configurations - 4.7, 4.6, CivicSpace - and tooled around with it a bit. (My new user sign-up is only because I lost my old one - and can't even remember which email I used to sign up :)
On the multi-site bit, here's what I'd like to accomplish:
1) User-based content promotion - Global and Community Based.
The problem with myspace, blogger, and crap like that is that peopel create content - but there's too many damn people, so no way for their content to ever get noticed.
To defeat that problem, I'd like to set up both community-based and global listings, where various "creative" is promoted by users rating each other's content.
Basically, on the "main" site, you'd have the global "best of" arts, music, humor, politics, etc. etc.
Then, on the "daughter" sites, you'd have community based "best of" arts, music, humor, politics, etc. etc.
It seems pointless for people to bother creating content and for it to just sit out in the void. I'm hoping there's a way to manage this through drupal.
2) Event Listings - Community Based.
I'd like for each community to have its own events calendar. I'm not sure whether I have to install CivicSpace to accomplish this or not? I'm not really sure what their CRM does at all, to be completely honest.
3) User Templates
When someone signs up under a particular community (subsite), I'd like for a theme to be automatically assigned to them, based on their location - after which, they can choose from any theme they like.