BiG Thanks to hugo! "To have a unified search" - that make things clear now :)
I got my site's searching against a single model work with writing lookup_kind function like yours! Now I can search for stories with query_string = 'kind:storys foo bar' and search for users with query_string = 'kind:users eric hsu'! That's pretty cool! However, here comes another problem: How could I have different templates for the search form/results? For example, I would like to have a simple search box on the top right of my frontpage, the user just types in the keyword(s) and then the search engine "default" search for stories and list the result in a story listing page; then, the user goes to another page which display a form in which he can type in keyword(s) and search for users, then the search engine returns the results in a user listing page which is different from the story listing page. Is it possible? btw, I'm not a native English speaker, I'll try my best to make myself clear :) Regards - Eric