McDonalds in this country is appalling, both quality and service wise. Went to McDonalds about a week ago to grab a bit to eat with mates as i've not had one for ages. The line was that long it was nearly to the door, after about 5 minutes of waiting in line we finally managed to order our food and were then told to wait at the side as it wasn't ready yet which was another 3 or so minutes. Can anyone tell me why it's called 'Fast Food' in this country? Because all we seem to do is wait about 10 minutes to get served and in that time you'd have been better off buying a sandwich which would have been quicker. Mate went to China/Japan (can't remember which one) a few years back. Went into a MNcDonalds there and apparently if you have been waiting longer than 1 minute then the food is free.
Maybe you should try and do the job for a week and you'll understand why it sometimes takes a while to get your order. Special orders, awkward customers, new staff and other things such as running out of food stock on the shop floor can all contribute to waiting times.
You talk of customers queing to the door, if you had any idea how much money McDonalds spends on reducing service times you'd be amazed. Next time you're waiting for a while to get served or for your order just take into consideration why it may be.