I was just asked to help in the investigation of a bank robbery. It appears that a former auto insurance customer somehow left her insurance papers in a car she sold in the glove box of a car. The documents were from 2009. Now, in 2013 a bank robber used that document to write a demand note on the back to hand to the teller. Now that customer is being implicated in the robbery as an accomplice. I'm sure she'll be exonerated, but, the hassle and defense costs will be enormous.
It's a really good idea to clean out your car before you sell it of any sort of document that might be used against you at a future date.