Will's take on ILC 2005 includes a breakdown of the types of people attending that seems pretty accurate, including these two:

The Ex-Lispers. These are people who are use to use Lisp, maybe even love Lisp, but don’t use it anymore. For some reason, several of these folks were plenary speakers.

The Yeomen. These were people who use Lisp to write large-scale projects used by thousands or even millions of people, or that have a significant, or even huge, impact on the world. Unfortunately, there wasn’t anyone like this.

Also, I wasn't sure if the lone female attendee Will mentioned was in fact an attendee, so I guess I feel better about that. I think I remember at least two or three women in New York in 2003, which means we're losing women at the rate of 0.75/year. Plan accordingly.