To my expierience (since 2009), ANC works really great with steady tones such as the constant humming on a passenger plane or the motor sound of a sports plane.
But for voices, walking steps of folks, cars around you: not so much.
Active noise cancelling should only really be needed in very loud environments, like the subway. In an office you should be fine with a well fitting set of closed back on/over-ear headphones.
I have a pair of Denon AH-D340 and I can't hear a damn thing with them on, even with a noisy conversation happening right next to me. I use them at 1/3 volume on my macbook most of the time. They have a lovely flat unhyped response as well, despite being styled after beats by dre.
If your office is as loud as a subway, my heart goes out to you.
Those fancy in ear monitoring ones are probably even better, but I personally find them uncomfortable.
There is a sound to active noise cancellation systems. Not really white noise, but a sort of faint, high-pitched noise.
It's not audible in airplane or other loud environemnts, but I never understood how you can work with that in your ears. Apparently some people doesn't find it irritating. But make sure to try someone else's before you spend hundreds on dollars on one for the office.
Purely anecdotal, but in my opinion in-ear-monitors (like the Sure or Etymotics) are much better at blocking out sounds than an active noise cancelling headphone like the Bose QCs.
