When is an advertisement not an advertisement? When Twitter says it's an "interesting topical experience." That's what cofounder Biz Stone, who once promised Twitter's website would never carry ads, is calling Microsoft's ExecTweets.

Stone declared some time ago that Twitter.com would be an advertising-free zone. But as Peter Kafka points out on MediaMemo, Twitter has been running house ads for some time, promoting its search engine and other features.

ExecTweets is a directory of business executives who use Twitter to post short messages to their friends, fans, underlings, and sycophants. What did it take to put Stone in that last category? Why, just a little bit of cash, courtesy of John Battelle's Federated Media, an online advertising agency known for its controversial online campaigns which blur the line between editorial content and advertising. Battelle writes:

Twitter has a history of promoting applications and projects they think are interesting, relevant, or valuable regardless of any financial arrangement. Federated Media felt that Twitter should share some of the revenue associated with ExecTweets since this project is made possible using their open platform.

He'd have us believe, in other words, that Twitter is promoting ExecTweets not because it's getting paid but because Stone and company just love, love, love it. Right. And if you believe that, Battelle has an interesting topical experience to sell you.