A few notes about Poker Room Bonuses:
Bonuses are one of the tools that online poker rooms use to entice players to play at their room, instead of at a competitor's room. In the brick and mortar world of poker, it isn't common to have the dealer hand you extra chips throughout your session. But, online poker rooms do just that.
They will offer a Welcome Bonus that is a percentage of your first deposit. And yes, in order to "get the most out of it" you should make the maximum deposit. It may sound like they are trying get more out of you, but 100% of $600 is $600. 100% of $400 is $400. You would be leaving $200 on the table. That's very "un-poker player".
The bonus money doesn't land in one lump sum, and except for at Bodog, it doesn't com e up front. (Bodog does give new players an up-front bonus of 10%, which is very cool). Instead, the money generally sits in a "bonus account", and is transferred to your player account as you play hands. Once the money is in your player account, you can cash it out and use it to buy pizza.
At one point in time there were so many poker rooms online, and so many bonuses available to online poker players, that some players made money every month grinding away and collecting bonuses. They took to calling themselves "bonus whores".
While you may no longer be able to whore your way to a paycheck every month, you can still take advantage of the Welcome Bonuses offered by PokerStars and Party Poker. And, you can expect the rooms to offer you the occasional "Deposit Bonus" to keep you happy and playing at their room.