I'm working on a network of sites, each running on their respective domain, and i'd like the sites to have a common user database. In other words, the users should be able to comment articles and post in the forum without registering multiple times.
One of the approaches i'm considering is to have a standalone forum (like SMF or phpBB based) and integrate the WP instances through a bridge. The other one is this new multisite feature (that i'm totally unfamiliar with), i suppose it'd allow me to use an integrated forum plugin like simplepress that would be available for users registered to any of the sites. The only downside might be that as i read somewhere MU requires a whole lot of resources, it won't even run smoothly on a shared hosting and needs a VPS.
I'd highly appreciate any advice.