Not just software stupidity.
last year an accuread man took a meter reading from my meter (i had to fill in a card because I was apparently "out" when he came round, despite me hearing the card come through and my car being on the drive, and him having to walk past the gas meter). I filled the card with the correct readings, and the meter reader then duly entered completely different ones on his little device when he could be bothered to actually turn up and read my little card. I got a £3000 bill, and it then took several calls to e.on before one of them looked at the numbers and suggested that it was a little "unusual" to use that much energy in a month. I noted they were very keen to get a correct reading this time around though (entirely coincidentally my bills will be going up by 15% or so, so they will be sure that any overestimate was nullified before the rise).