As the original site says, this is a chance for people with a common interest to get together. Rather than once a week, we do this once a month, on the third Tuesday of the month. As long as you have an interest in programming for Apple devices, you share that common interest.
Whatever you feel comfortable with. Sometimes laptops or iPads/iPhones come out to show off something cool, or to ask for advice about a bug. Or people just talk about things the way that you normally would do in a pub.
All sorts. Independent software developers, Contractors, full- and part-time Cocoa(-Touch) developers, students. People who's day job is Windows, but are interested in writing software for Apple devices.