The development team behind search company Inktomi is launching a new service tonight called Diddit, which functions as both an activity guide and a way to share stories and accomplishments.

Diddit is a bit like business-rating services such as Yelp and Citysearch, but with a broader range of listings, and a dash of “story-sharing” sites like Tokoni. It includes individual attraction descriptions as well as lists of everything from Harry Potter books to free activities in San Francisco. You can check off each activity as “diddit” (get it?) or “wanna,” and share more detailed reviews or stories. Users also have individual profile pages listing their “accomplishments” and their comments.

I have to admit, my first reaction to Diddit’s concept was, “Boy, that sounds awfully Web 2.0” — or, to use an insult that I’ve been seeing in VentureBeat comments and elsewhere, it sounds awfully 2008. I mean, is now really the time to launch a site featuring user-generated content, particularly one focused on travel and activities, and one that expects to make money through advertising?

But there are a couple of distinguishing features here. For one thing, Diddit’s content isn’t purely user-generated; the activity descriptions and the lists are actually created by data Diddit acquires from crawling the web, then fleshed out by users. That means the Diddit site is already pretty rich, even though it’s been in invite-only testing until now.

Second, Diddit is relevant even to users who don’t intend to spend a dime on recreation in the next few months — there are plenty of free activities, plus you can brag about things you did in the past, when you might have been more flush with cash.

Finally, the basic Diddit interaction is surprisingly addictive. As silly as it might seem, I get a real sense of pride from checking things off the lists. It’s the same social mechanism that drives the “things I’ve done/books I’ve read/movies I’ve seen” memes on blogging communities like Livejournal.

Diddit already lists 300,000 activities and has 10,000 users who have checked off 750,000 activities. Now that the site is open to the public, one of the next steps is to integrate with social network sites like Facebook and Twitter.

Ludic Labs, the San Mateo, Calif. company that made Diddit, has raised $5 million led by Accel Partners, with participation from KPG Ventures and individual investors.