The Enneagream is a very interesting personality typing system. I learned about it when I was at Santa Clara University. It is similar to the Myers-Briggs system, except that I find it to be more nuanced and focused on motivations rather than behaviors. It approaches personality from the perspective of a person's "worldview." This helps explain why two people who seem similar on the surface are sometimes quite different after you get to know them.
There are several interesting authors who have written books about the Enneagram. My favorites are the Riso/Hudson books. They have a new book out called The Wisdom of the Enneagram, which is quite good. Here is a link to their web site, if you are interested in learning more:
You would be suprised to know how many people use the Enneagram to understand personality. There has been a PBS documentary on the Enneagram and I have seen it discussed in child development lectures and used by lawyers in their practice. Although it draws off of ideas and theories that are hundreds or thousands of years old, some of the Enneagram treatment today is still a bit "new-agey." However there are several groups, including Riso/Hudson, that are trying to take a more rigorous approach to it.
Bottom line, I think it is worth checking out. Reading about the Enneagram can help you understand yourself. It can help you understand others also, though it is easy to cross the line and "type" other people, thereby putting them in a personality box. This is a slippery slope. It is best to focus on understanding yourself, how you operate, and how you are motivated on a deep level. As a side benefit, you'll get a deeper understanding of others.
Other Enneagram web sites to check out include: