Header spacing issue after upgrading to WP 3.1

I upgraded all of my blogs to the latest version of WordPress (3.1)

I noticed that after upgrading, a large space appeared above the headers on my websites. If you go here: https://isthatweird.net in Google Chrome, you’ll see a gray space above the logo and advertisement. While this doesn’t happen in Firefox, on my other blog I had the problem where the large space appeared in Firefox but not in Chrome.

Any idea why this is happening and how I could fix it?

Thanks in advance for your help.