questionme-
Here is an example of multiple account abuse.
1) Deposit 5000 each in two accounts.
2) Get the extra signup bonus.
3) Bet on opposite sides of same games, and feed winning money to losing account.
4) Build deposit bonuses on the transferred money.
IF the bonus program is too generous and the juice too low, it is possible to gain some advantage, particularly if a book allows occassional free payouts. It is still a lot of damn work, and you are screwed if you are caught. However, there are "players" that look for stuff like this.