I've been using the List api in my app, and just noticed that the POST method to /:user/lists.:format returned the correct response, but didn't actually create a list.
I've been following this api document: http://apiwiki.twitter.com/Twitter-REST-API-Method:-POST-lists What I did notice was that the Add New List ui on Twitter.com has a description field, and so I tried the same call with an additional post param "description", and it worked. The description param can be empty, but it is required to make this call work. Might be a bug? Just a heads up for anyone who might be wondering. DC