Does anyone have a clear view of Twitter's Terms on commercial use and can clarify it? For example, Flattr and Ribbon.co have recently run into trouble, but Ch

Does anyone have a clear view of Twitter's Terms on commercial use and can clarify it? For example, Flattr and Ribbon.co have recently run into trouble, but Chirpify, Amex and Dwolla look like they might have Twitter's blessing. Can anyone give a good explanation of how it works?