Felix Salmon wishes Twitter a happy birthday with the observation that it's gotten more annoying and will grow even more annoying in years to come. I think Tom Lee nailed the basic dynamic about two and a half years ago, these things come in grand cycles:
Here’s how it goes. First, a network achieves viability — enough people are using it to send non-”hello world” messages that the community can sustain itself. Next, users experiment, publishing and republishing content that they find compelling. The system amounts to a collaborative filter, and the quality and novelty of the results are surprisingly good. At this point people begin to notice and discuss the potential for the network to have greater relevance — and, inevitably, those who don’t understand that participation in the filtering activity is non-negotiable begin whining about taking the medium seriously when they see so much trivial content on it. Despite this carping, more users join the network and its value and potential importance begin to be more widely understood. At this point users change how they identify content worth publishing or republishing: rather than the first-order “how compelling is this?” they begin using the second-order “how compelling will other people find this?” Although they were excellent and determining what they thought was interesting and appropriate, they’re comparatively terrible at determining what other people will like. Quality declines (“I blogged: del.icio.us links for 2009-07-02″). Worse, as users continue to try to shirk their collaborative filtering responsibilities, experimental uses of the medium are discouraged or otherwise become less viable. The system ossifies, and soon enough everyone is sick of having to check Facebook. Time for a new no-pressure medium for goofing off with your early-adopter friends. Rinse, repeat.
One way to think about it is through the organization of the workplace. Once some medium becomes widely used enough that it becomes someone's job in many organizations to manage the institutional account and encourage reluctant staffers to use it, you're past the "joyful" phase. I still like Twitter a lot just like a like blogging, but neither is as fun as they were when they weren't conceivably part of someone's job.
But I do hope we can save Twitter from Salmon's prediction of "getting serious about making money, which means selling us, the users, to people willing to pay lots of money to work their way into our timelines one way or another." The better approach would be for Twitter to ask people to pay for their service directly, in exchange for a commitment to maintain its quality. This is especially true because the Twitter ecology seems very well suited to a tiered pricing model. You could let anyone sign up for a free "basic" account, and then say people who want to amass more than 1,000 followers need to pay for a "pro" account and establish additional increments at 10,000 and 100,000 followers. That way the bulk of the users keep using Twitter for free ensuring that the large network is there, and then the minority of large-following people who are using Twitter to gain access to that audience pay the freight to keep the system up and running.