We pretty much always return our cart to one of the corrals once we are finished. That being said, we don't really do much grocery shopping like that anymore. We basically just pick up our groceries and someone in the store does the shopping for us. For a while we were having them delivered too, but that got expensive.
That sounds pretty sweet. We don't have that in Japan yet. I'd be afraid though of the clerk picking all the bruised fruit and boxes/cans with dents on them. Hmm... I have teenage trust issues, maybe.
They tend to do a bit better than you would think. When they deliver even more so because they get tips. When you just pick them up at the store, they aren't allowed to receive tips. Which is really nice these days!