hi, i'll agree at my desk it is quite often difficult to see all the bags and pax do tend to put it infront of my desk so that i have to ask to see their hand luggage.
The airline i deal with regulary has a 5kg limit. but most pax say "they said it was for the cabin when i bought it"..... my answer.... i wouldn't want that on my head if it fell out!
i like my boss' motto. if you can't lift it properly it goes in the hold!