I got it several times a couple of hours ago, too, but it happened only some of the time. Refreshing the page sometimes worked and sometimes didn't. So this seems like quite a vague problem for Jordan to pin down.
I'm afraid I have no idea what could be causing that problem. More interestingly, as I see in your screen shot, the search box which is supposed to display under the banner ad is missing, but the "Advanced" link remains, minus the parenthesis which should be surrounding it...
The next time you see a page like this, please click "View" in Firefox and select "Page Source". Save the source code in a .txt file and attach it to a message here so I can take a look at it.
I've started seeing this as well, and it looks like there is something wrong with the ad code. I'm working on a fix now...