>>Keep in mind that JB runs a user group and lives very close to major cities

Even if it's the same presentation every time, it's still a big commitment. Especially when the ground is moving so quickly and many developers already have experience with Android and/or iOS, meaning the usual "stay 5 pages ahead of the pack and you'll sound credible" isn't as easy to achieve. I'd say JB is putting a lot into it and if he's getting that many invitations I would not be surprised if/when he moves on from a salaried developer job to be a mentor/consultant/trainer. A certain other PA crew member managed to achieve that and has told us more than once of the financial benefits and other satisfactions, so I guess that person won't be surprised either. ;-)