Keep Calm and Carry On

What's with all those "Keep Calm" posters? I've been pondering this for a while now. I've always thought they were fun and creative, but what I didn't know is that there's a history behind it. Watch this video (I promise it's not bugged or inappropriate or anything-- I got it off YouTube):

So now that you know the history behind all the slogan, I'll share a few of my favorites: