I have a policy of increasing the number of posts on the Internet reflecting good customer service, so here's a positive note:
When returning our rental car at 3:00 AM after our vacation in Washington earlier this summer, there was no apparent request for dropping off any documentation or place to do so. Just a number of lanes to leave the car in.
A week later I got a bill for $61 with no explanation of what it was for. I went to their web site and, with some difficulty, sent them a message.
It took five weeks but they did eventually get back to me. The charge was for fuel, despite the car being returned with a full tank. Looks like their after-hours return process assumes that you'll be filling out and dropping off a form. When someone did close out the rental, they didn't acknowledge that the tank was full. The good news was that they did refund the incorrect charge. For some reason it took another week for the refund to actually process, but their email predicted that, so that was OK.
It wasn't the smoothest rental I've ever done, but it did get resolved correctly. I won't be avoiding Hertz in the future.