Should the validations section use the new style?

In Rails 3 we have a new validations (http://
edgeguides.rubyonrails.org/3_0_release_notes.html#validations)

eg. validates :vote, :presence => true

My understanding is that the old style eg. validates_presence_of will
still work.

The guides still refer to the old style - should they be updated?

Yes they should, please feel free to edit any old-style macro via docrails.