My company do this, but the system is based on a PDA, not a laptop. The customer receives an invoice by e-mail, which still goes through our office. The system is a lot quicker for us, as shown if we have a terminal PDA fault, andbhave to go back to paperwork! For the customer a big benefit is we can give a fairly instant estimate for any further work. Parts and labour prices are built into the system, so no adding up for us, the PDA does it. In most cases the customer will decide to OK the work there and then, thus avoiding a drawn out process of getting the office to send out a quote, etc. Also built into the system is our actual levels of van stock, which is updated daily. So it knows what you should have, even if you've forgotten. Customer details, from address, phone number, contacts on site, contract details, are all there, as are details of all trucks on site. When we have a job for a particular site we can enter jobs on other trucks without having to contact the office again. Parts lists and tech info are included too, though this is one area where the bigger screen of a laptop would be more useful. All in all though ours is the best overall computerised system I've seen. I still use a paper diary as backup, though!