I've seen several posts lately where people were given rental cars with expired registrations and for some reason, instead of writing the ticket to the car's owner they give it to the driver! Which makes no sense but I guess it's easier for the cop.
As you can imagine, often the rental company says Yeah yeah we'll take care of it, and they don't, and then people discover their licenses were suspended because of the unprocessed ticket.
And while you're doing your walkaround at rental time, make sure to pop the trunk. If the car has GPS, make sure there's a CD/DVD in the player which is often back there. And lift the carpet and look for a spare and jack; if they are there make sure they're in good nick, and if they aren't at least now you know if you get a flat.