I do a lot of my work from the cafe at Barnes & Noble, and I routinely walk away for extended periods of time, leaving my laptop sitting on the table, my car keys and wallet in my backkpack beside the table, and a cup of coffee sitting there. I've been doing this routinely for well over a year, and I've never had any of my stuff messed with.

Maybe I've just been lucky, but I don't really feel like the crowd of people who come in there contains a lot of people who are going to try to steal a laptop or anything. And there are usually plenty of people around, and I've gotten to know a lot of the other "regulars" so that probably helps as well.