How to Power-Tweet from an RSS Feed Reader
This video demonstrates the power of Lobster (an RSS feed reader that's part of Blog Riffer) and its Twitter plugin. The blogging, Posterous, and Tumblr plugins work in much the same way, but have additional options.
Since this video was made, Twitter made it impossible to subscribe to your "friends timeline" RSS feed using a username and password (you have to go through a Twitter API client). The way to subscribe to your friends' tweets now is to create a Twitter "list", add the people whose tweets you want to read to it, and then subscribe to the list's RSS feed (which doesn't require a password or any other authentication.)
Posting to Twitter still works as shown in the video, or you can schedule tweets for later, and have them posted automatically at the specified time.