Direct messages can start piling up in Twitter, and I don't always have time to look through each message (especially since 95% of them are spam).
Here's an easy way to mark all Twitter direct messages as read, with one click.
First, open your direct messages by clicking "Messages" at the top of your Twitter home page.
You'll see a popup screen with a list of your direct messages. Click the "Mark all as read" button at the top center of the popup screen.
That'll mark all of your Twitter direct messages as read, in one shot.