All good points. The only thing to add is that there is no formal Aerobatics Qualification from the CAA/JAA. Legally you can just hop in an aerobatics aircraft they day after you obtained your PPL paperwork and do a few loops.
Obviously that would not be wise and that's where AOPA, Ultimate High, BAeA/Loop beginners day and so forth come in. My club also has a lesson plan, separate checkout and a fancy certificate for anyone who wants to do aerobatics.
And as the previous poster has said, if you learn aerobatics from a licensed instructor, the hours count for your PPL. But remember that since there's no formal license for aerobatics, the person who teaches you aerobatics does not have to hold an FI ticket.