I had these headphones for a couple of months and would say the noise cancellation works well for most ambient noise (it works extremely well for low pitch noises but most high pitch noises will not be affected) and although the sound quality is not amazing, with the $50 price tag I would not complain.
I actually broke mine today and stumbled across this price whilst looking at replacements - I purchased mine for $75 no longer than 6 months ago.
Personally, after using these I would prefer to go for the Logitech UE6000 when it was on sale for $88 at dick smith, but it has now returned to $198. I will be looking for other headphones in the market but I would recommend these for those who don't care too much about sound quality to pay over $100 but care enough to not purchase cheap in ears. Good for train/bus commuters too - using headphones on the train without noise cancellation is just uncomfortable for me now.
Be wary of those who would like in-line microphones built into the headphones- there are none. The wire itself is actually very long too if you don't like that, and it is my main problem with it. The reason why it broke in the first place was because it got snatched on a table while I was walking out of a lecture.
Plenty of stock around Victoria, not sure about other states.
Noise cancellation headphones for a lecture - money well spent :)