There are all kinds of bonuses offered at various sites. How good a bonus is depends on the level of game you want to play. If the site requires you to contribute to the rake it will take a lot longer to clear a bonus. If you need to play 2/4 tables to qualify for an hourly paid-to-play bonus, then you will never get it if you play .50/1 limit.
Read the terms and conditions of the bonus before you make your first deposit. How long do you have to clear it? Do you have to contribute to the rake for a hand to count or is the fact that it is raked sufficient? Is the bonus paid per hour for the first 5 hours a month of play (William Hill for example) and what limits do you have to play for them to count?
The Cryptologic sites (Interpoker, William Hill, Sun Poker etc.) have standing offers for propositional players, but you have to be willing to play heads-up at 2/4 limit or higher. If those stakes are outside your comfort level, then it isn't worth the effort.
In terms of bonuses, you want to take full advantage of good sign up bonuses so it helps to have the maximum deposit available. Otherwise, you want to have enough on deposit at the site so that you can sit at the table with a reasonable bankroll and handle the variance without going bust.