I have a buddy who runs the websitehostingdirectory.com – very bright guy in terms of SEO & he has said to me that .com & .net domains are ok but that other extensions do not get picked up as much by the search engines. I do think that if you are trying to geo target that a country extension works ok, for instance for uk web hosting on this result
http://www.google.com/search?sourceid=navclient&aq=t&ie=UTF-8&rls=GGIC,GGIC:2006-37,GGIC:en&q=uk+web+hosting there is only 1 site in the 1st 10 results which is not a UK domain (although they are a UK based company)
But looking at generic results like:
http://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GGIC,GGIC:2006-37,GGIC:en&q=web+hosting
there are no domains in the first hundred results which are non .com /.net or .org(omly 1 .org)
Good luck in your search