Who ever came up with the idea of "brown bag" sessions was smart. The idea behind them is that it is an informal seminar / session to convey information. The concept is that attendees get a packed lunch either themselves or supplied - comprising of cut sandwiches, and maybe some fruit and a drink. Attendees would then eat while participating in the session. Used correctly, it could be an efficient use of what many would consider a lost hour.
While this is good, I believe it falls down on one key point. People value their own time. And if you are cutting into someone's lunch time, you should give them a benefit. I am not referring to the benefit of gaining more information, but something more tangible.
Something that organizers of these events should consider is providing the lunch to the attendees - not relying on the attendees to bring their own lunch. More people may then be interested in attending, and it would offset the feeling that attendees are loosing an hour of their own time. I guess this would be a different view if people worked in hard labour / sweatshop conditions, and personal lunch time is a rarity.