The street food scene has exploded in the last two years, with a new food truck being born every day. But just how far this trend can go? Is it sustainable? Are we witnessing gridlock? If there's one person who would have some thoughts on the matter, it's Matt Cohen, the 31-year old founder of the SF Cart Project and Off the Grid, the mobile street food market. We caught up with Cohen after listening to him speak on the future of food trucks at last week's Commonwealth Club event "SF Street Food Update."