I see QR codes everywhere. Does anyone actually use these things?

I've never scanned a QR code in my life. My band is trying to convince me that they could be a good marketing tool, but I disagree. Most phones require you to download an app to scan them. Do people really use QR codes? Have you ever scanned one or seen anyone scan them?

For anyone who doesn't know what I'm talking about, it looks like this.