I generally fly a fair bit but am not obsessive about it. I hate checked luggage so I squeeze my needs into a 60liter backpack and head off to where i need to go. Sometimes that bag weighs a good 40kg In some cases I came back with far more than I started with(read: 2 60 liter bags!) and still stuffed it into the overhead luggage while the attendants watched and snickered to each other. No harm no foul.
In North America, Asia, Europe and Africa I have never had a bag weighed. When I asked about this i was told the weight restriction was all about whether you could stuff it in the overhead compartment w/o help, they knew the plane could carry it. i guess I always looked like I could handle the bags and so far have never been bothered.