RE: Pulling forward.
If the cashier is on his toes this shouldn't be a problem - most tills use Edacom or Meggit fuel delivery/till systems which are capable of storing 2 seperate transactions on each side of each pump. Actually, if it's really busy you can transfer one over to the till side and suspend it which means a total of 3 transactions "saved"
We used to get large lorries filling up, and with a 100 litre cut off they'd have to restart the pump a few times so I had to handle this type of transaction a lot. It shouldn't really cause any bother if the cashier is paying attention, though it CAN get a little complex when people forget how much they put in and you have 2 amounts "flashing" to be tilled in.
RE: Pump pipes damaging the car when you are using the "wrong side"
Never ever seen this happen, the pumps are made of relatively soft plastic material and I don't see how it could cause damage to a car body unless you started whipping it with some serious gusto. Also, if you pull far forward enough you can bring them round behind the boot where they barely touch the corner of the rear 3/4 panel. Hell, you can hold the pump in one hand and lift the hose clear of the body if you're really worried.
RE: People paying in shop when they are using pay at pump tills:
Like atpbx, this really gets on my ****. These lanes are normall marked as "Express Lanes", they are for people in a hurry who want to use them as they are intended. I actually think stores should remove the "pay at till" option from them.