It's the latest meld between social media and online advertising: ads that appear in Twitter feeds, along with updates from real users. It's called in-stream advertising, and it makes the line between social networking and social advertising even tougher to distinguish. In-stream ads are only available to advertisers with "promoted accounts", who pay for visually highlighted ads that show up with traditional Tweets from individual or business users.

Why are some companies paying top dollar to place their brands' message in Twitter feeds? Any Tweet is only as big as its reach. Regular users must build their following by waiting for other users to find and subscribe to their Twitter account. Promoted accounts are actually suggested to select users - those who have expressed an interest in that brand or in related brands. Twitter automatically generates lists of accounts that users might want to follow, based on their current usage. Promoted accounts appear at the top of these lists. According to Twitter, this strategy builds user followings for these accounts faster than traditional methods. It's good for the overall ad campaign, too. The promoted account is reaching a self-selected demographic - users who have an active interest in consuming the product or brand advertised. Users feel they're receiving a benefit from subscribing because it allows them access to deals and promotions that other consumers don't get.

In-stream ads represent a major shift in online advertising. Ads no longer appear beside the content, they are the content, and because of the way Twitter has designed its in-stream ads, they are always relevant to the user. Tweets from promoted accounts can use this level of familiarity with followers to build brand relationships. For example, a recent promotional Tweet from Coca-Cola asked users to submit their "favorite retro jingle or slogan" and they would be entered to win a prize of Coke paraphernalia. This kind of Twitter ad doesn't tell the user directly to buy Coca-Cola, but it reminds them of the ongoing relationship they have with the brand. One could assume that the contest itself is a way for Coke to gather data about its followers and market to them via email or other means.

Revolutionary as in-stream ads may be, they are still ads, and today's consumer is more adept than ever at ignoring them. No data exists yet about the efficacy of in-stream ads, and they may not catch on if Twitter users express a dislike for them.

The development of in-stream ads does prove this: More than ever, advertisers are focused on reaching targeted audiences online. Online - whether through a website, Facebook page or Twitter account - is still the best place to reach new customers. The idea, just as in traditional marketing, is to get the name out there, build familiarity with customers, and sell the brand, not the product.