Twitter has started rolling-out advertising on the site this week, with Disney-Pixar's new animated movie Toy Story 3 becoming the first 'promoted' trend.

On the right side of a user's Twitter page, Twitter lists its top 10 topics or trends, basically a list of what users are tweeting about most. As of Thursday this week, an 11th trend was added with a yellow banner beside it, saying, 'Promoted'.

Toy Story 3 is released in the US this weekend. Users that click on the promoted trend are taken to the latest tweets about the movie, with a promoted tweet from the advertiser appearing at the top of the search results page.

"Promoted Trends are a new advertising concept we began testing this week; they are an extension of our Promoted Tweets platform," the company noted on its website.

"With Promoted Trends, users will see time-, context- and event-sensitive trends promoted by our advertising partners. These Promoted Trends initially appear at the bottom of the Trending Topics list on Twitter and are clearly marked 'Promoted'. As conversations about the topic increase, Promoted Trends may move up the list."

The company also said that if a topic isn't already being tweeted about, it cannot be a Promoted Trend.

Twitter didn't say how long it will test the new ad feature, saying that everything depends on how successful it is.

Ezra Gottheil, an analyst with Technology Business Research, said the ads are a smart move since they give Twitter a revenue source without drastically affecting the user experience.

"People will tolerate advertising as long as it lets them do what they want to do," he said.

"As with Google, users know someone has to pay. Users prefer it to be painless. Advertising that doesn't get in the way is generally welcomed."

The promoted trends come on the heels of Twitter's announcing in April it was rolling out 'Promoted Tweets'.

'Promoted Tweets' give organisations the option of purchasing a 'tweet' that will appear as the top result when web users search for words and topics on the site.

This is similar to Google's sponsored links that appear at the top of results pages generated by the search engine.

However, Twitter said, initially, only one 'Promoted Tweet' will appear in each search results page and they will only be seen by around 10 percent of the Twitter users.

The company had been criticised for becoming wildly popular without the backing of a business plan. Last October, Twitter CEO Evan Williams told an audience at the Web 2.0 Summit in San Francisco that the company wanted to focus on developing the site rather than on a business model.

However, in April, Twitter finally took off the training wheels and moved into the world where real businesses tread with the launch of its first advertising model.

See also: No ads for Twitter this year