Maybe it's just the stores I've been to that have slow self-checkers, but I bet they take roughly the same amount of time (if not longer) than a regular checkout, it just feels like it's a shorter wait because you're doing something other than staring at the cashier while they ring up your groceries. My personal pet peeve is people who block out the credit/debit machine after they've been rang up, preventing the person behind them from running their card. It seems like it mainly happens at Target where the end of the checkout is both where the bags are put and the card reader is.