What's the hottest API on ProgrammableWeb today? It's the Twitter API. This is not surprising to folks tracking the latest news on Techmeme where hardly a day goes by without another Twitter-related headline. And indeed we're seeing the impact here on PW, with a large spike in the number of Twitter applications being added to our directory. Just look at today's entries where all three of the new mashup listings use the Twitter API. We now have 120 Twitter apps in our directory.