Doorways have been abused greatly in a few industries such as real estate, hotel services, and adult content. All these industries reach out to a large audience, so it may be easy to find abusive pages for their topics, but the search engines are always on the lookout for new abuse. They will ban domains and IP addresses to stop the abuse. There are programs which create doorway pages for you. As the search engines change their ranking algorithms old doorway pages become less useful.
Some people study the search engines to determine what designs work best for each engine.
Such analyses include determining the percentage of text devoted to the keywords and phrases in high ranking pages. There are even tools on the Web which assist such analyses. Be careful of using the doorway generators. They utilize templates and include standard comments in the generated pages which the search engines can identify. Some of the templates have been identified with the result that many Web sites have been dropped from popular search engines.