I've read they're taken very seriously in some places like Germany and Japan, but in my experience, a lot of people in the USA won't bother reporting noise violations because they know the chances of them being enforced and/or investigated in a timely manner is low.
Enforcement in Germany is quite funny. Lived there for some years.
If you have a problem with noisy neighbours you basically must make a "noise diary" with date/time/description of the noise over a period of time before anyone will give a shit.
Even then, enforcement varies wildly. Seems to depend where you are, etc.
The best person to complain to is building management, but even then, they vary.
The next best thing to do (and the most German solution) is leaving passive aggressive notes on the buildings noticeboard.
It depends, of course, but yes, I have had noise complaints addressed by some kind of code enforcement officer (i.e. unarmed, but able to write citations.)
