Twitter has rapidly become my new addiction -- its a really cool way to stay in touch with friends and if you turn off text message notification and use something like twitterific I've found it is actually quite usable. One thing I just don't get is the AS2 and AS3 libraries they released, instead of simply parsing your RSS feed for messages it uses a JSON parser class. Talk about overhead -- that doesn't make any sense to me. This is one of those situations where they try to shoehorn an AJAX approach onto Flash. The example FLA that comes with the library also has code embedding your twitter username and password to get hold of your friends timeline.
While I understand they want to keep the example easy to read and understand, that's not a smart move! How easy is it to decompile a SWF, get hold of account details and start spamming away?
If you need to do anything other than what the RSS feeds can get you, I'd really recommend using a server-side script to proxy the calls rather than running the risk of exposing your account details client-side.