To fully understand what Kickback bonuses are and how they work, it is important to know a little about the Affiliate industry. To put it simply: Poker Rooms need players -> Affiliates find players for Poker Rooms -> Poker Rooms pay the Affiliate.

A common method of rewarding affiliates is CPA or Cost Per Acquisition. This is a one-off payment for referring a qualifying depositing player. Kickback bonuses are perks given by Affiliates to the players they refer, as an incentive for signing up, usually in the form of extra cash.

This is in addition to any other bonuses you may receive from the Poker Room itself. Seeing as the kickbacks are usually in the region of $100, you can see why they can add large amounts to the winnings of a low stakes player. Imagine getting a few buy-ins for every site you sign up at!

Obviously, there is a catch... Poker Rooms do not want players just depositing, receiving a kickback, and withdrawing. This is why every deal has requirements. You need to earn a set number of points or raked hands before you can receive your kickback. Luckily, the requirements are always quite low. In the Kickback Bonus section, you will see each deal has an Optimum Bonus and a Maximum Bonus, each with a Clear Rate. The Clear Rate is an approximation of your return on Rake paid while clearing the bonus. For example, a bonus that rewards with $200 in total and requires $100 in Rake, has a Clear Rate of 200%. In almost all cases, the Poker Room itself offers its own Bonus, too. These are always much larger than the kickbacks, but are much harder to clear. For example, this Full Tilt Poker Kickback Bonus requires 250 Full Tilt Points to receive the kickback. However, the regular Sign-up bonus requires 10,000 Full Tilt Points to clear in its entirety! The optimum bonus is the amount you would receive if you quit immediately after earning the kickback. In this case, you would get $15 from Full Tilt Poker for the 250 FTPs and $120 from the Affiliate, putting the Optimum Bonus at $135, with a Clear Rate of 378%. No matter how many FTPs you earn, this is the highest Clear Rate you can achieve with that deal. The maximum bonus is the amount you would receive if you clear the entire bonus, which has a Clear Rate of 50% in this case

Rakeback is simple: Either your Affiliate or the Poker Room itself gives you back a percentage of the amount you Rake at the tables.

There is more to it than that, though. Firstly, some sites base your Rakeback on Gross Rake, while others base it on Net Rake. The difference is that the latter will deduct cleared Bonuses and sometimes even deposit fees from your Rake and giving a percentage of that number instead. Instead of sharing a part of their turnover with you, they share a part of their profits.

Secondly, there are 3 different calculation methods for Rakeback.
Dealt Rakeback: Rake is divided evenly each hand among all players at the table. This favours tight players.
Contributed: Rake taken is divided evenly each hand among all players who placed a bet. This favours loose preflop play.
Weighted Contributed: Rake is divided according to the amounts put into the pot by each player. This favours loose postflop play.