We are moving to Cancun in a month, and we are driving. We have been studying up and talking to people that live in different parts of Mexico. What we have found out is....the roads in some parts of Mexico aren't to good, big pot holes and speed bumps in the middle of highways. Also, it is illegal for the police to try and bribe you, but they still try. Take a camera and if you get pulled over for no appearant reason, get out and start snapping pictures. They will leave in a hurry if you've done nothing wrong
We were also told to have an alarm system and a club on your steering wheel, mexicans won't steal it if they have to work at it. There is no more a chance that you will be ripped off in Mexico as there is here. Just better safe than sorry. And renting a car in Mexico isn't cheap either.....and gas isn't as good as it is here. Drive during the day and you don't get robbed. No different than some parts of the US.
Mexican people are great in general, but like all tourist areas, they see us coming ! English is spoken in the resort areas and it's not hard to communicate anyway.
Don't listen to idiots that say Mexico is corrupt. That's a bunch of shit, things don't work exactly like they work here, but why should it.