That completely depends on the type of building. I'm in a NYC high rise that is poured concrete. I can't hear a damn thing. Once in a blue moon the people upstairs drop something and I hear a thud, that's about it.

I have previously lived in some hilariously thin walled places before. I actually think the 2-3 story apartment rows in suburbia are the worst offenders. If you are building a 20+ story building, you have to make it a bit thicker and use steel or concrete.

I wonder how this differs by area and building type. My apartment walls in the Bay Area were razor thin - I couldn't believe how much could be heard. But in the four apartments I've been in Manhattan (all ~50-100 years old), plus a good friend's new high-rise that I frequent at all hours, I've never heard my neighbors.

In fact, in my current apartment I have not once heard my roommate when my door was closed despite the bedrooms sharing a wall.

Like others mentioned, this largely depends on the building type -- e.g. concrete vs wood and gypsum. Most American apartment complexes below 5-6 stories high are usually all wooden with low sound proofing.

For what it's worth, I'm in a newish (2010) apartment building in Berkeley. It's one of those wood and drywall jobs, and we never hear anything from neighbours except those above us if they drop something or stomp.

Perhaps this building might be unusually well built. All the windows are double-glazed for example, which is definitely not needed for climate reasons around here (Berkeley has to be one of the mildest climates on Earth).

Having said that, this building is mostly populated with moneyed students (the garage looks like a BMW/Merc/Audi/Porsche showroom - factory stickers are common). I imagine they're not the noisy type. We're a family of 5 where the kids have done things like use skateboards indoors, so perhaps our neighbours are cursing us for the noise :).