From Guy Kawasaki's blog, a new study by Frederic Lucas-Conwell looks at what a technical evangelist is and what motivates them (us).   Here is the abstract from the study:

The purpose of this study was to gain a clearer understanding of the relatively new phenomenon known as the “technology evangelist.” By our exploration, we aim to help readers improve their management functions, and to understand how best to integrate “evangelists” within their organizations.

In order to do so, we analyzed the roles of those who hold this position and leadership styles. Our research included surveying and interviewing twenty-nine technical evangelists worldwide from a variety of cultures and organizations. Some general tendencies regarding the role did, indeed, emerge. However, we also discovered variable character, or personality, patterns among the participants. Therefore, we proceeded to examine the gap, between the role of the technology evangelist and the subject’s personal character.

We contrasted individual competencies with these character patterns, and created a grid to analyze their qualities of leadership. This paper includes our recommendations for recruiting, integrating, developing and managing the technology evangelists.

Frederic interviewed evangelists from Adobe, EBay, Google, Sun, Microsoft and Yahoo in the study. 

If you are interested in evangelism, you should definitely subscribe to Guy Kawasaki's blog.  I like to follow his blog, and recently I saw him present at the GNOTE Conference in San Jose.  He's a very good presenter, and he's considered the first "technical evangelist" by many.