I have a friend that really likes them. He lives in an apartment that has noise problems from upstairs neighbors, and he said they totally cut out all that racket.
I also read a review of all noise cancelling headphones online somewhere, I forgot where, but they also tested them against earbud types (I think someone else posted something about that here) and the consensus among the "audiophiles" was that the high end earbuds costing around the same as the Bose noise cancelling headphones did a much better job of eliminating outside noise than any of the headphones tested. In addition, there was no loss of sound quality, and in fact they rated the high end earbuds as having much better sound quality accross all frequencies.
I have a pair of Aiwa noise cancelling headphones that I think were about $60 and they do eliminate outside noise quite well, but when switching them on they seem to "boost" the signal somewhat, and there is a feeling of pressure in the ears. My friend says that "pressure" feeling is also there with the Bose headphones (he tries on my Aiwas too). Noise cancelling is just reporducing an out-ot phase signal to moise picked up by the headphone mic, so that pressure may be due to the activation of the headphone speaker even with no input signal. I can tell you that the Aiwa phones start feeling a little heavy after a while, and after listening to them for an extended period, I start to get a sense or irritability. I have read reports that "bad" sound can have that effect on one mentally.
I tried Bose headphones in a local store, and I personally didn't like the way they sounded. Seemed to lack good bass response, but that may have been the listening source.
All in all, it may just be a matter of personal preference at the bottom line. Doesn't Bose offer a 30 day trial period in their ad? I seem to remember seeing that.