At home I vote for the Green Left

( I took this political test at OkCupid... )

And now I have a question for the US-people on my flist: I understand you need to register to vote, do you have to do this before every election? Did you register? If not, why not? Do you still have time to do that?
In the Netherlands we are registered at birth and you receive an invitation to vote for any kind of election from the day you turn eighteen. You don't have to vote, for government-elections there is a 80% turn up. I understand a much lower percentage of Americans bother to vote, that worries me.