As many have said, it is generally felt that Bose products are overpriced for what they offer. In my opinion, this doesn't necessarily mean that all their products are bad, but they do seem to be universally too expensive.
All of Bose's headphones (and probably most of their products, for that matter) are sonically outclassed by better, more obscure headphones on the market. However, because of their advertising, nearly everyone has heard of Bose. I don't think there are many people who haven't seen a Bose ad, but if you asked most people about the SR80is or D1001s or ATH-M50s they wouldn't have any idea what you're talking about. In addition, Bose's headphones are quite comfortable, and they sound a lot better than crappo stock iBuds. I suspect that many people hear a Bose headphone as their first "high-end" upgrade over the stock iBuds, and they fall in love immediately and probably don't even bother demo-ing many other headphones before buying Bose (except maybe the Monster Beats, another real winner). This accounts for the amount of 'phones that Bose is able to sell.
But yes, the reason that people don't like them around here is because they do not perform to their price level. And the reason they get hated on so much (in addition to Bose-bashing that happens just for jest and sport) is that they represent a general ignorance of the common market when it comes to audio. We here at Head-Fi are audiophiles, we love sound quality, and it pains us to see that a company can dominate the headphone market through the quality of their advertising rather than the quality of their product.