Powering multiple blogs from one installation

My understanding is that it’s not yet possible to power more than one WP blog from a single installation, right?
The reason why I ask is because I’m thinking about starting up a couple of new sites, each with a blog, and I was thinking how annoying it’d be to have to update and/or hack each WP installation separately.
Ideally, it’d be wonderful if one WP installation could power multiple blogs (and on different domains). For instance, I could control a blog on both https://www.foo.com and https://www.bar.com from my single installation at https://www.adamswordpresssite.com, by having both foo.com and bar.com import entries via php includes. And best yet, it’d be neat if within one WP installation, we could specify different style-sheets and behaviors per blog, too (just like MT in this case, though MT lacks what would be a very handy “use this template for all blogs” feature ??
Is this all entirely wacky, or do you see some sense in what I’m wanting?
And either way, how would you recommend currently structuring the implementation of multiple blogs on different domains, while minimizing the time required to fuss with WP upgrades and such?