From Twitter today:
For this reason, aside from Promoted Tweets, we will not allow any third party to inject paid tweets into a timeline on any service that leverages the Twitter API.
What does this mean? If you are a user of sites like Sponsored Tweets, then you can't use them anymore unless they change how they operate. Twitter's post doesn't explain who they are going after — I'm guessing its the companies making money. My problem with Promoted Tweets is that it doesn't do the user any good — just big name companies with open pockets. I don't make a cent off of it, Twitter does. I don't know — it seems to cross the line into stealing content because I don't think they ask your permission or anything to use a Tweet you've done and turn it into a promoted tweet (I could be wrong and if I am please correct me).
That being said — I've added a new category to my advertising/media kit. If you are a company looking for somebody to Twitter for you (I've got over 20,000 followers!), please head over there!