I think there is a penalty for showing Googlebot something other than what people can see, but these sites all use tricks to get around it by allowing users to

I think there is a penalty for showing Googlebot something other than what people can see, but these sites all use tricks to get around it by allowing users to see the same thing as Googlebot in various circumstances. For example Quora has the ?share=1 URL variable. The Wall Street Journal allows users to read a limited number of articles for free if they clicked in from Google (tracked via a cookie). The New York Times allows free reads from anywhere for a limit, but also tracked via a cookie. LinkedIn blocks their registered users, which is probably the worse system ever.