I once got caught at Air Canada upon checkin for a flight to SE Asia. I had my two checked bags and my carryon bag and a PURSE. The representative at checkin, made me weigh my PURSE and my carryon bag. Of course, I was well over the weight limit for carryon. I complained that the weight was supposed to be for the carryon bag only, and she said NO, it is for all that is carried on.
This has never happened to me again, but I live in fear. :P