Hmmm... What I do know about ignore functionality is that you won't see anything someone on your ignore list posts in the 3 main chat channels (general, PvP, trade) and won't get any tells or whispers from that person and won't get matched with that person in groupfinder. Apparently ignored characters can get grouped with you in warzones.
What I'm not sure of is if someone on your ignore list is in your guild (
) is still visible when they post in guild chat. Also I don't know if you've ignored someone but they've got you on their friends list will get the notification when you log in.