According to sources with AllThingsD, Twitter is expected to hit around $350 million in ad sales this year. One of the largest drivers for ad sales is more precise ad targeting and the removal of arbitrary limits on the kind of Twitter ads that businesses buy are being changed. Advertisers now have the ability to target Twitter’s 140 million active users with Promoted Tweets. There is no longer a minimum price for bids either — Twitter is now charging per “engagement,” which means replies, retweets, and bookmarking. Twitter has 350 “interest categories” so that advertisers can target ads to followers of a specific account. If you like this news article, you may like Mitt Romney Campaign Is The First Political Campaign To Spend Money On A Twitter Trending Topic.