Much commerce depends on offering different deals to different sets of customers, to extract the highest price from each individual instead of relying on the "market price".
Airline tickets are a good example.
In such markets, there may be an advantage to consumers banding together to aggregate pricing information. If all users of priceline style "reverse auction" or whatever they call it shared bid info, it would turn it into a "treasurys style" auction where everyone got the best price that gave the seller the required volume of sales.
Another way to break the attempted segmentation of a market is to make the product fungible, so that a secondary market develops if there is any inefficiencies in the first market. It used to be common to re-sell unused airline tickets via newspaper classified ads, and airlines got rid of that after Flight 800 blew up (because of electrical failure) on anti-terrorism grounds. You can get back the exchangability of airline tickets through some tricks, and sell and buy airline miles on sites like points.com and flyhub.com, but that must account for a miniscule part of the market.
Back to deleting your cookies to compare amazon and hotel offerings -- wouldn't a firefox plugin that showed you what prices other people were seeing for rooms or books or whatever, when you browsed to that page, be pretty useful ? Maybe it could be monetized by commission or referral fees of some sort ?