Just when you thought Twitter was a relatively harmless social networking site, here's what they do. They'd originally started with promoted trending topics (which are paid for) and promoted accounts in the “Suggestions for You” tab (which are also paid for). Now they're putting full-on advertisements in between tweets, ON THE TIMELINE. Basic bombardment. They're supposed to roll out ads already.
They're starting out with testing this via a third party application, Hootsuite. Hootsuite has two versions, a paid and a free version. The paid version, of course, comes advertising free. The unpaid version (at least on this reporter's account) didn't have advertising yet, which means it's rolling out in phases. After testing this out on Hootsuite, the ads will eventually move to other third party applications and finally the Twitter.com homepage itself.
The problem I have with this is how intrusive it is, based on Twitter's format itself. With Facebook, the ads exist in a sidebar. You end up seeing them but they don't get in the way of you looking at the general content of the site. On Twitter though, when they're interspersed with tweets, it could get very annoying. I'd much rather just see the promoted trends in the sidebar and know where Twitter's getting some $$ from.