Matt,

In your account setup (Update your account) check 'Move replies to your messages to read as soon as you read them' and don't worry about that anymore.

>How can I just mark a message as Read while I am reading it?
>
>I usually just click on a message in the Sidebar under the Replies area (without actually opening up the entire Replies page), and it shows it to me, but there is no way to mark it read right then. There are other icons in the toolbar when viewing a message by the method, like Save and Delete, so why not one for Mark as Read?