Would this be on or off-topic? Somebody's rare work, prints' availability, techniques, setups, books?
Think this depends entirely on the question. Photographers may only be famous within a specific territory.
Questions of the form of "I like how [Will Cheung/etc.] achieved [effect X/etc.], I've tried doing [approach a/b/c/etc.] but have been unsucessful. How can I achieve [effect X]?" are going to be more obviously on topic than "What do you think of [Will Cheung/etc]?"
This seems for the most part to be on-topic, but we have to be very careful when defining "Famous" photographers. For instance, Henri Cartier-Bresson or Ansel Adams are clearly famous, and known of by most photographers, but what about someone like Kiino Villand who is a professional with some notoriety, but is probably not actually known by a majority of photographers?