> Self-checkouts don't have to suck, though. The version where you scan all your items at a single location is clearly crap, but there are systems where you get a small hand-held device when entering the store so you can scan your items as you go along.

This is presumably much better for throughput, but much worse for making sure that what you're leaving with is what you purchased. (Also, how does it accommodate a decision to put something back? I've never seen such a system.)