If you don't know what a QR code is read "What is a QR Code and Why Do You Need One?" or also, this article in FastCompany from last year is great (and also a reason why you should go to SXSW Education or Interactive this year) "What Business Card? Just scan my QR Code." And of course, you can always go to Wikipedia.
Here is a tiny glimpse of what our front page looks like. I am restricted in what I can do since this is only part of a bigger site but you get the picture. If not, check it out here. LibGuides actually has a nice mobile version so students can use their phones. I just discovered this when I created the QR code. A lot of our kids have smartphones and tend to work on the bus to games or what not. A lot of our students have iPads as well. I hope that when the new iPads come out with the camera feature, students can also scan these QR codes.
If you want to read more about how libraries are using QR codes, check out LibSuccess.org's QR page. If we had historical buildings we could actually put QR codes with the history of our campus around for when people are walking around campus waiting for their tours. But we are middle school so that might be a bit too much. I also was thinking it would be a great way to familiarize our kids about the library by using it for a scavenger hunt. Most of the libraries featured on that wiki page are universities but I don't see why it wouldn't be great to use it for a school.
Are you doing anything with QR codes at your school? I know one school is using it to promote books on their newsletter to parents.