Startup Idea : interest-ad

Declare your interests to receive useful ads = such a handy network. Users have smartphones, PCs, etc. By means of a special app, they can declare what their interests are: to buy something, to visit some place, etc. They just describe the interest in words, additionally some location information may be included and so forth. On the other end, server-side, all declared interests are accumulated. And it is possible to search through that accumulated stuff. Therefore manufacturers, producers, providers can easily learn what there's a demand for. Moreover, they can send out ads that will only be delivered to those users who have previously declared appropriate interests. (If spammers exist, users will be able to influence them: educate and/or ban.)