Inspired by this, just how useful are programming conferences of various types? What do they offer that you can't get from just reading and researching subject online?
The most valuable aspect of programming conferences for me has been the networking: the opportunity to meet peers outside my normal 'social' circle and discuss problems, solutions and approaches. At conferences, that group often includes the speakers themselves so you get a chance to discuss issues with experts in various fields.
In addition, taking you physically outside your normal working space has the effect of letting you reset your environment for learning, forget about your day job (to some extent) and focus on trying out new things in a collaborative, hands-on space. Even if the sessions themselves are not hands-on, conference attendees will generally try out at least some of what they're seeing during conference.
For me, a good programmer's conference once in a while "raises the bar" (once a year?).
Working at my job, head down, day after day, I only see what those around me can do. Getting to rub shoulders with people that come from a completely different perspective and others who are just really smart - is inspiring. It shows me what could be done. Different ways to solve a problem.
I prefer shorter, smaller format conferences - less than a week. With a week-long conference, you tend to experience the "4th day mind overload". With larger conferences, I find that it's harder to get to know people.