My Webware colleague Don Reisinger would get a kick out of TwitteReader, a new and free service which turns Twitter into something resembling Google Reader (something he's ditched entirely in place of Twitter). Once you've plugged in your username and password, it presents the latest tweets as individual feed items, which you can cruise through either by reading the short snippets (a la Google Reader) or expanding them out to full posts with a click.
Just like Google Reader and Gmail, you can move up and down the list with the same J and K keyboard shortcuts. You can also star items, which adds them to your Twitter favorites list. The application keeps track of what you've read and what you haven't, which, depending on how many people you're following, could be useful. If a system like Google Reader's trends were to be applied to this you could see which people's updates you're not reading and cut them out of your followers list.
Of course the obvious must be stated here--you can simply take the RSS feed of your friends provided by Twitter and plug it into Google Reader to accomplish something quite similar. TwitteReader's killer feature, however, is that it lets you post and reply to messages from each post, just like you would in Twitter.