I've only been through the drive thru, but I've visited pretty frequently. It's almost always the same staff in the morning, and they're always smiling (nice to see in the early hours). I've only had the wrong order once of the zillion times I've stopped by. The credit card machine was down once, but it happens.
It's mcdonalds. If all you can really ask is to get what you want from someone who at least seems happy to help you, then these guys are doing their job!