Hit up the Facebook, Plancast, EventBrite, and Tweetvite APIs (others?) to pull attendee (or at least those who showed an interest in an event) lists and collate those users for event organizers. If they created a Gowalla Event, pull those who checked in. Build Twitter lists of those identified in relation to the event.
This is a need right now, methinks.
Known implementations: None
With Facebook now offering a Like button for web sites which posts back to Facebook and helps with ad targeting…there’s a giant sucking sound towards Facebook (to paraphrase Ross Perot).
But I think there’s a lot of value in collating people’s likes/hates/mehs for any web page out there on the Internet, regardless of Facebook’s plans.
Maybe it’s just me.
UPDATE: A couple of people have pointed me to http://openlike.org/ . Neat idea. What I am talking about is building a site (like a StumbleUpon, I guess), which collates likes/hates/mehs for the entire web. This site could accept logins from Twitter, Facebook, others, so that it leverages existing networks.
Known Implementations: None