In reply to minimike:
My sister had an awful run in with Hertz in Australia when they hit a kangaroo - can't be bothered to recount the saga again, but took a few months to sort out before they backed down and admitted their error. The kangaroo was ok, though.
I also had a bit of a run in with them (Sydney branch), when we arrived to collect our hire car, having pre-booked a child seat. Apart from the huge queue, which we hadn't been expecting, once I'd finished the paperwork, I had to go and get the car from the storage car park, navigate round an unfamiliar one-way system to get back to the office to get the car seat fitted - all of which meant we were about 2 hours late meeting some friends for lunch. So much for efficiency and customer service (they had all the info they needed about the child seat on the booking form).
On the other hand, the lady in the Adelaide branch couldn't have been more helpful and didn't charge us for the car seat because my daughter gave her her best smile at exactly the right moment.
Best experience I've had was Enterprise in Florida. Car we started off with had a steering problem, so took it straight back - chap in the office said no problem, grabbed a handful of car keys, walked me out to the garage and said take your pick
Unfortunately, I'd left my sunglasses case in the first car and never got that back - at least I'd been wearing the glasses.
Edit - I always take detailed pictures of the car and wheels before I even get in it and do the same when I return it.
Post edited at 11:55