You have to use different ip's and cookies create a problem. All accounts can get the captcha thing. It depends on alot of factors.
Definitely marketing wrong. On myspace today, doing bulletins for marketing isn't very effective. It used to be when myspace was vulnerable and it was easy to multiply bulletins like a worm, but this is fixed now. The "friend-adding" and sending out messages is useful as well but links are checked by myspace. It has became much more difficult but myspace shouldn't be considered ineffective as far as advertising goes. There's people to be reached, it's just up to you to come up with the method.