I actually get a little stressed when I arrive with a cart full of groceries and an empty line -- they ring them up at about twice the speed I can pull them off the cart.
The Aldi process is very well thought out. They're the only cashiers I've seen that sit in a chair while ringing things up. They needn't move, nearly at all, beyond swiping things past the register to read those giant barcodes (on anything store branded, which is most things). I remarked to the cashier about their ridiculous speed and was informed they are also tracked, directly, on their speed and have targets to meet (and incentives if they're "the fastest").
[1] Their produce is consistently good (love the sweet, small, green grapes) and their Frozen Chicken Nuggets are better tasting than any I've purchased, including the organic ones at Costco.