Originally Posted by Aviatrix
Most European carriers have weight restrictions for carry-ons (I am only aware of ONE that doesn't - Easyjet).
Most, if not all European carriers use the weight concept rather than the piece concept for checked baggage.
This means that unlike American check-in counters European ones are equipped with scales - making weight restrictions quite easy to enforce. (I was quite surprised the first time I checked in for a flight in the USA and found there were no scales at check-in...)
All checked baggage gets weighed at check-in, and there are weight spot checks on carry-ons - if something looks heavy they'll usually weigh it, if it doesn't they usually won't.
No scales at check-in? I've never checked in baggage without having a scale. It's just not all that obvious--the place where you hand the bag to the ticket agent is actually a scale.