According to Reuters, Twitter is about to test an automated system that will allow clients to schedule their own ads. Currently, an advertiser has to talk to a human in order to get that Promoted Tweet in the stream, but this new offering will allow clients to set up ads on the fly and change them on a whim.
For Twitter users, this isn’t good news. Twitter is a relatively small system. There are only a few places where you can insert an ad and for those who don’t follow a thousand people, an influx of Promoted Tweets is going to be very noticeable. I’d hope that there is a safeguard that would keep the ads from being the majority of any stream, but maybe not.