Dumpster diving is not by nature stupid, I think. Tim Horton's, a chain coffee & doughtnut shop up here, throws away all of their doughnuts at midnight, to be able to maintain their 'made fresh daily' claim. Having worked at Tim Horton's, I totally think it is fine to take those surplus doughnuts at quarter past midnight, just check the bag first so that you know they haven't also dumped chicken salad in there as well (but that is unusual).
Just as a rule of thumb, if there's food in a bag, and there's nothing else bad in the bag, it is safe. If you are adventurous, you can even wash of sketchy produce, but I avoid anything suspect, myself.
Roo, with regards to the person who thinks it is immoral to eat dumpster food as it deprives hobos, I would say buy a hobo a doughnut and offer that person a dumpster doughnut. If they still refuse to eat it, then I would assume they are just afraid of dumpster food and are spinning an argument to defend their position.
Food not bombs is pretty sweet as well, I have helped cook for them once and it is super fun. Where I am, we make two batches of soup with what we've got (both vegan) which we just give away to anyone who wants some. The philosophy, as I've come to understand it, is that instead of building bombs, we should be making soup and building community. You meet cool people when you're in the kitchen, and you meet cool people giving food away on the streets. And it is not just for the homeless, everyone can eat if they want food.
I dislike the notion that taking from a store's dumpster is robbing them of the sale, though. If they are throwing it out, then I have no problems with taking it. To hell with them wasting it out of spite. If they want to offer it at a discount, I will probably buy it. If they want to throw it out, I may well take it.
P.S. Regarding video cameras, my major coup when I left Tim Horton's was sneaking out like three boxes of instant cappuccino, hot apple cider, and hot chocolate with the trash. I later swapped some with my friend for subway southwest sauce. I was a good, reliable, experienced worker who had trained people I was making like ten cents an hour more than. Fuck those guys.