Whether your cabin baggage gets weighed really depends on what airport and what airline you are flying with. With most full-service airlines, they don't bother weighing baggage as long as it meets the size restrictions - and sometimes they don't even check that. The bit about size restrictions is because at some airports, at a security counter itself they flag oversized items and ask you to go back and check it in instead. Usually, there are metal enclosures which they place the baggage into - if it fits, it's good to go.
With low-cost airlines, it's a bit different. In Europe, I have seen they mostly just care about the size rather than weight. In Asia though, low-cost airlines sometimes do also weigh to see if its within the weight limits. The reason why I said it depends on the airport as well as the airline is because, just to take an example, if you're flying out of Singapore's Changi Budget Terminal used by low-cost airlines then there's a centralised size and weight check carried out by airport security, and anything (visibly) overweight is weighed and excess baggage fees collected. Flying with the same airline at a different airport (on the return flight) the other airport may not do the same check.
Don't worry about this too much. The size and weight restrictions, as most airlines mean it, is more as guide for what can safely be stowed in overhead bins or under seats. Most airlines understand that sizing is not standard, so weight is a 'safer' way of defining a guideline of what you should be aiming to carry on board as luggage. As long as it's not visibly bulky, airlines and airport security won't stop you or charge you extra fees for carrying anything onboard.
