SDS-
The problem with opening more than one account at a book (as regards bonuses) it that some books offer higher bonus on INITIAL deposit and then lower for subsequent deposits. Thus, multiple accounts not only give player extra bonuses, but cost the books extra money if they cover deposit fees.
Bonus whores are also players that come into a book, play out the bonus, then withdraw and jump to another book as soon as they see a shinier bonus program.