This all seems to vary by which part of the world you are in.
In Europe only small hand baggage is allowed, the airline actually manages this, and anything larger will be taken off you at various points. Despite this the overheads still seem full, but mainly of coats, laptops etc.
In the US larger items seem to be permitted, most annoying of all those Wheeled Wonders which their owners cheerfully scalp the heads of their fellow travellers with as they struggle to put them up into the bins. There's a certain mindset become associated with these where the possessors of them then have to ram down the throats of their fellow seatmates how clever they are not to have used the checked baggage service.
In Asia it's even more astonishing. People buy things like boxed television sets in the Duty Free shop, after check-in, and then bring them aboard.
Having seen an in-flight severe turbulence encounter where the bins opened and items that really should have been checked came down and injured passengers to the extent we had to make an en-route landing and those people were taken off to hospital, I've maybe seen a bit more than most.