I can be listening at low to moderate volume levels and watch people talk without hearing them. The only time I hear talking is if it's loud or my msuic is in a very low point or silence then I hear the talking as whispering. To give a specific example, I was on the train staring down at 2 girls who were having a lively discussion giggling and laughing and all I heard was my music while listening to some classic rock at about 1/3 volume on my Nokia 920.
I have demo'd these to over a dozen people and I do it by turning off the unit and ask them to put the earphones in. Then I simply turn it on and in every case they are STUNNED! I then play some music . The thing that is so amazing is the amount of ambient noise these remove. Things we have trained ourselves to ignore, things like the air conditioning fans in buildings, the constants buzz when walking around a mall, etc, all of this sound simply falls away...
The new Bose commercials exaggerate the silence a bit but they are pretty accurate.
By the way these are a piece of cake to insert and remove making it easy to remove them when needed plus they have a button you can push that allows noise in which is good for when you want to talk to someone or possibly need more awareness.