I actually stumbled upon this when trying to find out what exactly got updated in the Google Sitemaps Plugin for Wordpress, but it's kinda neat. I'm not sure if I'll keep it, since I had a horrible experience with Outlook Express's preview pane back in the day, but here goes anyway:
1) Activate the preview pane for Gmail.
Arne's post says it works in Firefox, but it worked for me in Adblock for Chrome as well. I've found it a ton quicker to go through email that way.