Art manifestos still exist and it has become more common for fashion designers to use a manifesto to reach out with their thougts about their design and the world that their design exist in.
Vivienne Westwood is reading her manifesto in different venues in London at the moment. Have a look at http://www.activeresistance.co.uk to check out the next date and place.
Yves Saint Laurent, the people today behind the brand has followed the same path and is selecting a few large cities twice a year to hand out a fabric bag which includes their manifesto for the season.
Manifestos are also very common in the history of film. A director that not that long ago published a manifesto of a type of filming called "Dogma" was Lars Von Trier, in which he very cleary speak about the rules of Dogma and how it is the "only" way to shoot a film.