It depends. I think the problem most data websites have is that the user still has to do a lot of work to actually use the data.<p>Although not exactly a market, data.gov is a good example of what not to do. It is a gigantic list of datasets which is hard to search. Often the dataset is not in a usable format such as PDF or HTML, or it just links to another website which has a worse UI for accessing the data. The counter example is Factual which has a nice API and the ability to download their curated and cleaned datasets.<p>Many data websites are more like data.gov than Factual.<p>EDIT: I made the assumption you were asking about data websites. There are data markets that have existed for years behind closed doors between big companies. An example is health insurance companies buying de-identified health records for research purposes. As far as I aware, these markets are still doing well.