Twitter finally launches a paying business model with its Promoted Tweets.

It sounds pretty mild at the moment. About the only thing the end user will  notice is the occasional ad displayed on search pages:

You will start to see Tweets promoted by our partner advertisers called out at the top of some Twitter.com search results pages. We strongly believe that Promoted Tweets should be useful to you. We’ll attempt to measure whether the Tweets resonate with users and stop showing Promoted Tweets that don’t resonate.

Promoted Tweets will be clearly labeled as “promoted” when an advertiser is paying, but in every other respect they will first exist as regular Tweets and will be organically sent to the timelines of those who follow a brand. Promoted Tweets will also retain all the functionality of a regular Tweet including replying, Retweeting, and favoriting. Only one Promoted Tweet will be displayed on the search results page.

Early advertising partners include Best Buy, Bravo, Red Bull, Sony Pictures, Starbucks, and Virgin America. Get all the latest info on Promoted Tweets on the Twitter Blog.