Easier than the clickable world. Create a semacode now by using this Java applet called Web Tagger and download the software for your phone (assuming it has a built-in camera). When you shoot a semacode with it, the software acts like a barcode reader translating the code into URL and then loads it into your phone's web browser. Moreover, semacodes are not alone. There are other similar 'tags' derived from the same concept. Here is a list of the various kinds of tags in a technical entry made by Network Research.
Get the phone. Take a picture. Go online. Imagine how useful these things could be on business cards that link to constantly updated contact information. Another example could be, say you saw an advertisement and you are in interested to know more about a product and find out where to buy it etc. Thinking of a less commercial activity, you can print some of these for your friends and quickly swap blog URLs with each other. How about printing them on stickers? These are just a few that comes to my mind instantly.
What other applications can you think of?