From rake routes:

            user_cardset_default        /users/:user_id/cardsets/:id                               {:controller=>"cardsets", :action=>"show"}

>> rs.recognize_path "/users/mge/cardsets/zendikar"
=> {:action=>"show", :controller=>"cardsets", :id=>"zendikar", :user_id=>"mge"}
>> rs.generate :user_id=>"mge", :action=>"show", :controller=>"cardsets", :id=>"zendikar"
=> "/cardsets/zendikar?user_id=mge"