Common background noises such as typing or conversations between colleagues aren't attenuated quite as effectively. However, the dampening is better than any passive system and all it takes is to start playing some audio and it's enough that anything short of someone shouting directly at you will go by unnoticed.
Inevitably the addition of active noise-cancelling tech means the EP-3NC aren't cheap, but nor is the £90 asking price extortionate. The same amount of money would net you a set of Creative's own Aurvana In-Ear2 headphones and I don't think anyone could argue that the EP-3NC look or feel as nice. However, you only have to work in as noisy an office as the TR headquarters to be convinced that there are times when being able to more completely shut out the world is a definite good thing.
What is also particularly good is that as a result of the great noise isolation, you can keep the EP-3NC at lesser volumes than similar 'phones. I don't know about you, but I'll take all the help I can get reducing damage to my delicate eardrums.
It has to be admitted, though, that the outright quality of the EP-3NC's audio reproduction might leave you wanting a little. There isn't the same detail resolution or warmth as similarly priced earphones or even cheaper ones - the Klipsch Image S4's would give these a run for their money, were it not for their noise-cancelling prowess.
Up against the Etymotic Research hf2, for example, there's no competition on a quality basis, but you'll have to spend another £90 on custom tips to get the hf2's noise-isolation anything like on par with the EP-3NC.
It's not a particularly revelatory conclusion to draw, that a set of noise-cancelling earphones excel where the listening environment has a lot of noise that could do with being cancelled. It's good news for the EP-3NC, though, because it means they do indeed fulfil their intended function and performance in every other respect is entirely adequate.