Stephen Hackett wrote a short post last week about a couple of data points that make him worry about the future of Twitter. In addition to Stephen’s points, I'd add to the list a concern that Twitter is trying way too hard to turn itself into a Facebook-level revenue generator when, fundamentally, that’s just not the Twitter we all originally signed on for. It is this limited scope that makes me like Twitter, and the harder they try to become a huge ad-selling platform, the more turned off I get.
I'm not certain the service is doomed. This is probably wish-casting, but I believe Twitter could be more successful in the long run if it simply went back to he original vision.