I know we're talking about totally different scales here, but web users are able to be very, very fickle. Look at something like digg. In what seemed like a few days, the site all but completely lost all relevancy because the users' perception of "management" was that they were catering to advertisers.
Twitter could fall just as quickly (and so could facebook, despite what seems to be popular opinion) if the users start feeling like they have to be cautious about what they're tweeting (or who they're following, in this case).
I know we're talking about totally different scales here, but web users are able to be very, very fickle. Look at something like digg. In what seemed like a few days, the site all but completely lost all relevancy because the users' perception of "management" was that they were catering to advertisers.
Twitter could fall just as quickly (and so could facebook, despite what seems to be popular opinion) if the users start feeling like they have to be cautious about what they're tweeting (or who they're following, in this case).