No matter your school of thought on how you use Twitter, the list of people you follow now includes advertising. The first customer: MasterCard. On the web, and in the official Twitter apps for iPhone and Android, you'll find that you, and everybody else, have MasterCard as a promoted entry in your Following list.
Now, this doesn't mean that you're actually following MasterCard — they have just 388,000 followers and not the quarter-million user base of Twitter. It just means that MasterCard has managed to get an ad inserted in every following list tempting you to follow them back (at least on the iOS and web interfaces it's clear that you're not actually following them, the Android app shows the same checkmark button for accounts you're actually following and the MasterCard promotional listing). The left-to-fallow official Twitter apps for BlackBerry 10 and Windows Phone, however, aren't showing the sponsored listing, nor are third-party Twitter clients.
While for most of us that's not the worst thing in the world — you're not actually seeing all of MasterCard's tweets, it is an interesting concept for advertising, especially if you're the type that looks at the list of whom somebody else is following. MasterCard is there. Everywhere you look on Twitter's following lists, you'll find MasterCard. Even for Visa and American Express. We're sure they're utterly thrilled about that.
For public figures and companies that can create an interesting conundrum. Many are cognizant of what accounts they follow. As, of all people, William Shatner noted:
.@jack@safety Do you understand that by implying that I follow these companies that it appears to be an endorsement?
Some of suggested blocking the offending account, and it's true that it will remove MasterCard from the sponsored slot in your following list. Problem is, it's simply replaced by another entry like IFC.com.
So yes, your Following list and every Following list you see now contains ads masquerading as follows. You're not actually following them, and Twitter isn't explicitly saying that you are, but MasterCard is there, holding down a spot in your top ten most recent follows.