I recently ran across PMOG, and damn, I wish I’d thought of that! It’s a "Passive Multiplayer Online Game" that you play by surfing the web with their extension installed. You get points for each site you visit, and you can use those points to leave either gifts or traps for other players. There’s also user-created missions or paths that involve visiting other sites.
Why is this so interesting? It’s is a fantastic way to get permission to do interesting things with people’s browsing information. They get in-game rewards for sharing so there’s real reciprocity, you’re not just an evil corporation harvesting click-streams. Games are a great way to get people involved with a process too, with the instant rewards and status hierarchies that they generate. Even better, they’re free for the provider, all you have to do is provide fun and compelling rules. This means it’s a lot more likely they’ll be willing to provide detailed information about sites they’re visiting.
What could this mean in practice?
Site descriptions. You could get points for writing a short website description. It could be structured so that useful descriptions earn more points.
Comments. Contributing to a discussion attached to a website, through the extension interface, could also earn you points.
Rating. Simply giving a Stumbleupon style thumbs up or down to a site could get you a small amount of points too.
Provide information about yourself. By interacting with a site, whether it’s leaving a surprise or adding meta-information, you’re making a connection with it. You can mark that connection in a profile page, and build up a rich set of favorites.
This is the first compelling application I’ve seen that could persuade large numbers of users to happily share their browsing habits with other people. There’s only 4500 users right now, but I’ll be surprised if that doesn’t grow. Games are incredibly powerful motivator, if you can tap into the human instinct for play you’ll be amazed at how much work people will put in to achieving the goals set by the system.