If you use the Internet, there's a good chance you've seen or at least heard of the "Hitler Reacts" videos.
There are a ton of them. Just go to YouTube and search "Hitler reacts" or "Hitler's reaction" and you'll see videos of Hitler reacting to Rebecca Black's Friday, the iPad, the infamous Kanye West VMAs incident, Modern Warfare 3, the Playstation Network getting hacked, Michael Jackson's death, Osama Bin Laden's death, Muse albums, football games, and many other things.
Suffice it to say, it's a popular meme.
Naturally, the Google Panda Update has now been commemorated with one (I'm surprised it took this long). In it, Hitler is informed that his sites have been hit by the update.