YAPC has a normal attendance of around 300 people who, on average, vary in age from 18 to 49, though we certainly have a few younger and a few older than that. And around 90% are generally from the United States, while the rest are from countries all over the world.
Over 70% who attend identify themselves as System Administrator, Developer, Architect, or Technical Manager. We also usually have a handful of business owners and C-level positions in attendance, as well as a smattering of other titles.
Around 45% identify themselves as using Perl in an IT or Internet industry. Generally around 8% identify themselves as belonging to one of: finance, government, education, or media related industries.
About 35% of attendees have never attended YAPC before. However, over 95% of attendees say that they'll come again. Those numbers bear out, because around 60% of people who attend a YAPC have generally attended more than one.
For more hard data on YAPC attendees, checkout YAPC Surveys.