Why people go to events
I think people go to events for several reasons. But the biggest reason people go to events is to be with the other people at the event.
When you create an event, you are creating an ad-hoc network of people. A group of humans who are going to share an experience, and create relationships that would otherwise not be possible.
Hopefully they will learn something new, but you can teach courses online. If the point is to just learn about new techniques or tools, why travel?
So it matters who comes to your event. This is one reason we keep a guest list or our Tweet Houses. When we host a conference it costs several hundred dollars to attend, so the problem solves itself: the people who come are people who want to get something out of the experience, because they paid to attend. At a free event, we need to crete another gateway.
Just remember, if you’re putting together an event: the “who” is as important (or more) as the “what” and the “where.”