What's an accceptable level of carbs?

If you're on a "low-carb" diet? I was checking out some of those Atkins Diet bars, and they have quite a bit of carbs. I thought that diet was all about cutting out carbs? I have two friends who have lost a LOT of weight by totally cutting out carbs, eating only salad & meat. I'm trying it too, but I need satisfyings snacks too. Will a bowl of yogurt with 7 carbs jeopordize it? Or a couple crackers with cheese?