Keep your mouth shut. The owner may act like your best friend at times, but remember at the end of the day he is your boss. He most likely didn't become a multi millionaire because he or she was an idiot, so don't try and them as they will see right through you. Also, don't offer any information to them unless you are certain it is correct information. No what if's (outside of weather and mx).
Oh, and watch how many extra responsibilities you volunteer yourself for. You may feel like your getting a leg up, but you will regret it when you become the boss's personal ground chauffeur.
Seriously though, best advice I was ever given was to just keep my mouth shut, and do my job to the best of my ability.