As a rough guide I would say that about 5 % of pax on flights I used to operate would remove the safety card and browse over it. Most are complacent as 'it would never happen to them'.
The small percentage who would talk over the top of the demo would be kindly asked to zip it (to allow their neighbours a chance to save themselves if the brown stuff hit the spinny thing).
One guy unravelled his lifejacket to have a closer look, on top of being a little disruptive, and so was blacklisted from uk airlines for his return flight, and his friend disowned him! Luckily CAA regulations ensure many spare lifejackets and safety cards are carried onboard each flight. It is an offence to tamper with any safety equipment.
On Italian routes, we used to discover seat belts missing (they were taken as a fashion item as a belt). Unfortunately it resulted in offloading passengers for the return journey as the seats were unusable.
I have to say I much prefer seatpockets. As much as they are a pain to clean and ensure security, they also ensure that no loose papers and drinks cans are laying around the cabin, which is all it would take for someone to slip over when evacuating and block everyones escape.
Safety Demos? I used to read them and although not comprehensive, we had only a few mins to get everyone seated, secure the cabin and do the demo before we hit the runway. Sometimes it was like an SAS operation!!