Studies show that the average motor cycle helmet noise level is between 95 and 105 dB at 65mph due to wind noise. OSHA standards say that anything over 85 dB will cause permanent damage with long exposure. Anything over 35 mph can exceed the OSHA safety limit.
The argument is sometimes made that with earplugs you might not be able to hear horns sirens and such. My personal experience is that I still hear horns and sirens better than motorists riding around in noise isolating a steel cage.
I suppose a counter-argument could be made that once a rider goes deaf from the wind noise they won't have to worry about whether earplugs prevent you from hearing sirens and horns.
Personally I'll take the earplugs whether legal or not.
I have been using foam but am considering buying a set of custom musicians (high fidelity) plugs. Anyone have experience with those? Recommendations?