How to close message in preview pane in GMail

Are you a GMail addict like I am? Do you always keep your inbox open in one of your browser's tab? Do you like to experiment with new plugins and features that Google has to offer? If you do and if you've enabled a preview pane you might have noticed that after you read an e-mail, it stays open. I don't know about you, but that really irritates me. Today, thanks to this forum thread, I found a way to keep the preview pane empty!

Here's what you do:
1) Enable keyboard shortcuts
2) After reading your e-mail, press 'u'