For most of ProgrammableWeb's nearly six years, there were two things that always remained true about the mashup directory. First, that Google Maps is the most popular API used to create mashups. And second, that Flickr is a distant second, but well ahead of third. Recently one of these is no longer true, as the Twitter API has passed Flickr in popularity.
Twitter saw tremendous growth over the last two years, which ultimately saw it frequently one of the most popular APIs by mashup count each week. Flickr, by comparison, received much of its count in the early days of mashups, though it remains a rich database of photos. Over the last three months, we've seen six times as many Twitter mashups as Flickr mashups.
Twitter's other ecosystem
As a platform, Twitter is also exceptional because it's birthed so many additional platforms. Twitter-derived APIs are growing faster than mashups. This other ecosystem is fueled by apps that use Twitter re-sharing what they create, which is one of the Twitter tips from the guy who wrote the book.
Both Twitter ecosystems will likely see even more expanded growth now that Twitter is part of the iPhone.
What do you think has been the reason for Twitter's success as a platform? And why have developers cooled to Flickr, despite its potential?