As I see it, the Pirate Party is what the Green Party was in the 1970s. A party with a limited agenda but attracting mostly young voters because it feels cool, liberal and anti-establishment.
My second thought on this is that fighting for the preservation of the environement (the limited agenda of the Greens ...) is a lot more useful if not necessary, noble than fighting for free content on the Internet (which will not work anway).
But ... err ... I am the old generation here and my political preference goes to the Greens .