It's absolutely true. Driving around while sitting on my wallet is usually no big deal, but that is because my typical day consists of going to and from work and maybe running a few short errands. If it is a longer haul than about an hour, like to Ft. Meade for the rallycrosses for instance, being on the wallet becomes rather uncomfortable. A few times my leg has even begun to go numb. I have developed a habit of taking out my wallet first if I know I'll be driving for hours at a time.

As for leaving wallets and such in plain sight, I used to work at the Mayo Clinic here in town and once witnessed a doc's Ferrari F355 Berlinetta with a purse left on the front seat. That's just asking for it.