Twitter will make API changes on August 16th that break old versions of Tweetie for Mac. This update keeps the tweets flowing. Other updates:
* Increased security around your account.
* Disable posting to image hosts using the deprecated authentication method.
* Registration no longer needed. Section removed.
* In accordance with the Twitter Terms of Service, on July 1st Fusion Ads will no longer be displayed.
* Tweets no longer say they're from "Twitter for iPhone," but instead "Tweetie for Mac."
* An option in "advanced" to update your iChat status when you tweet.
* Improved Magic Mouse support.
So in short, tweetie for mac has followed the trend on the iPhone and is now free since it's supported by twitter. Some minor fixes such as updating the API and security, but I'm pretty happy that it's free now. Note that I've never paid for the registered version. Tweetie is now ad free. Though I'm still looking for a tweetie 2.0, and apparently the developer is working on it.