Hand baggage can be a problem on full flights but I don't believe it poses a safety risk. For those of you who are unaware, Airbus' own literature for the new style A32X interiors clearly diagramed how many pieces of hang luggage can be fitted in their lockers and as such they have been designed for that kind of capacity.
Weight wise, Easyjet offers unlimited weight within set dimensions but lets face it most peoples hand luggage will be of reasonable weight unless they decide to pack dumbells.
Crew, from my experience at Easyjet, do a great job at dealing with this. Oversized bags that are deemed a risk or simply too big which have been missed at the gate are tagged and sent downstairs (hold). Again from experience on the routes are operate this is relatively rare. Most hand baggage is within limits which means pax adhere or it is being dealt with at the gate. Furthermore handling agents at EZY have a matrix which, depending on pax load, sees X amount of permitted sized bags tagged free of charge and placed in the hold.
So the amount of hand baggage can cause problems and EZY have looked at several ways to alleviate this (including reducing bag size) but have so far deemed that such measures would impact on sales/revenue. However, at no point is hand baggage a safety risk IMO.
I sem to remember on my RAF trooping flights hand luggae was 4.5 kg and if over you unloaded till it was right!!
Pax on flights to Guantanemo Bay had 0.0kg hang baggage allowance. It's comparing apples with pears slightly.