I'd like to file an enhancement request:
I've spent part of this morning trying to catch up to my inbox and needed to go back through to mark everything as read, now. There's a button to do this on a per-page basis, but that limits it to 50 messages at a time (and that's assuming all messages on the page are 'unread' -- otherwise it reaches far fewer per page, of course).
I'd like a button that marks everything in your inbox as 'read' in a single click - perhaps with a prompt to confirm that this is absolutely what you really want.
I understand this might not be necessary for a lot of people, but I had almost 1,000 unread messages as of this morning and I bet many are far more swamped than that.