My husband saw this clay pot tower in someone's yard several years ago and I just had to figure out how to make one. I found some very limited information online and learned they were called Tipsy Pots. I also have full instructions on my website as well as a PDF Printer Friendly version of the instructions. This project has also been featured in the April/May 2009 Issue of Birds and Blooms.http://www.gardensandcrafts.com/tipsypots.html
This is a great way to utilize all those clay pots we gardeners sometime collect over the years. Having all the plants in one place saves time and water.
Also, don't limit yourself to just clay pots, you can use any relatively round object that has a hole in the bottom. I also made a neat version out of old tea kettles, which you can view on the website link I gave above.