Beer can chicken has something of a religious status in the barbecuing south of the United States. The basic idea is that you take a can of beer, drink a third of it (wahey) then place a chicken on top, so the legs are pointing down and the wings are pointing up. The whole thing is then barbecued.
It's a really good method for cooking chicken — it works well in the oven, too — but not for the reason people think. The general assumption is that the beer boils during the cooking process, which then steams the chicken, keeping it moist and tender. In reality, though, the beer never boils, and therefore imparts very little flavour. It’s also not clear why you’d want boiling beer flavouring your chicken in the first place.
The reason it is a good technique is because it cooks the chicken vertically, which crisps the entire skin of the bird at the same time as preserving all of its juices. That means you don’t need the can to contain any beer. Instead, you can fill it with chicken stock and you’ll have the base of a gravy once it’s cooked.