Feathers, flags, treasures - they're just time sinks to artificially make the game seem longer. Subtract the time required to find them all (even with the maps) and you get a game that is suddenly shorter than you thought.
Lengyel, magyar ket jo barat, egyutt harcol, s issza borat. -- Hungarians FTW! XBL/PSN gamertag: Poganin
Agreed with above, the game is full of pointless busy work to flesh out the rather puny main missions. If it weren't for all the additional challenges and collectables, it would practically only take a handful of hours to burn through.