[hastybuns]

It really does depend on what you're adding the nofollow to.

If it's for example a forum you're running and you might want to make sure people don't end up using your forum as a link farm of sorts, then absolutely nofollow those as it could end up backfiring.

Another reason could be if you have of software, or a template you've built on WP etc that has a link back to you at the bottom, you might want to nofollow that for the same reasons.

Otherwise, no, you don't want to nofollow all your links, you want to be able to tell Google which resources you find authoritative, so it can pass on pagerank etc.