Anyone who's flown much knows there is a wide range in baggage limits and also how much they are or aren't enforced by the airlines, both for carry-ons and checked baggage. In most places the enforcement is up to the airlines - at check-in and again at the gate. Some airlines are very strict (for example Qantas) while others are very lax (for example most US-based airlines I've flown) in enforcing their own rules.
Some airports, such as Melbourne Australia, have airport people checking carry-ons for size and weight before security or immigration, but generally if the airline has accepted it (or you have shiny metal baggage tags) they let you go through even if you have slightly more than you should.
But this may be about to change. The British Airport Authority (BAA), which runs most of the main airports in UK, has announced that from October strict new rules will come into effect. Before then they will be trialling the rules on certain airlines and flights.
I'll put the new rules about checked baggage to one side, since many airlines are in the process of changing their allowances anyway (at least for trips including North America where the piece concept applies). For carry ons, the BAA intends enforcing the size limit and number at security, including at transfers. In the case of London Heathrow this means a passenger may have arrived off an intercontinental flight with their carry-ons, then queued for a lengthy time at Flight Connection Centre security, only to be told they have to check their carry on and please clear immigration to do so. This seems absurd and can't possibly help the UK airports compete with the european hubs.
So I am going to watch developments with interest. While I dont go overboard with carry-ons, I would still be inconvenienced through greater queues, flights delayed to accommodate pax caught in queues or forced to clear immigration when they shouldn't have to, etc. If implemented as it has been reported to date, then I'll be looking to shift more flights to european hubs. I had been expecting to fly via London Heathrow more often now that Air New Zealand's new business premier is rolled out and especially with their London to Hong Kong flights starting later this year.