Paid Tweets?

Last night I found this message from American Express in my twitter feed.

Trouble is, I don't follow American Express and don't have any accounts with them. Nor do I follow any of the 34 people who supposedly retweeted this message. The tweet disappeared a short while later and isn't currently showing up in my timeline.

This is the new face of twitter: paid advertising within your twitter feed. According to Cnet, twitter is rolling out this new strategy this week, and users can soon expect to see unsolicited tweets from companies like Disney, HP and Pepsi.

I'm curious about what the response will be. I'm tending to move away from Twitter lately anyway and maybe others are too. Could this move help hasten their decline?

UPDATE (9/20): Now I'm getting these several times a day! Here's another one:

Hard as it may be to believe, I don't actually follow Dunkin Donuts --or any donut company. This is irritating.