Here's an example of a hand you would play very differently on the money bubble in a Sit & Go than in most other instances. You're second in chips with 3,000, the blinds are 100/200, and you're dealt Ad-7d in the big blind. The chip leader is on the button and raises to 600; the small blind folds and you call the extra 400. The flop comes Q-8-3 with two diamonds, which is a pretty attractive flop for your hand. You check, and your opponent does exactly what you didn't want him to do: put you all in for about double the size of the pot. You're getting slightly better than 3-to-2 pot odds on a call for your tournament life.
This is a situation in most tournaments where, if it was early in the Sit & Go or if the money bubble had already burst, you would call. But this is a special situation. You are on the bubble and 60% of the prize pool is about to be awarded. If you call here, you're probably about 50/50 to be the player that finishes on the bubble and gets none of that 60%. This is one situation where you need to really let the structure of the Sit & Go influence your decision.
Once the bubble bursts, your approach should change dramatically. Look again at the payout structure: the last three players are fighting over the remaining 40% of the prize pool. If you move up from third to second, you get another 10%, but if you move up from third to first, that gets you an extra 30%. That's three times more reward for winning in online poker tourneys than for just moving up a spot. So your goal now becomes to do what's necessary to finish in first place and not be too concerned about going broke and finishing in third.
You should be willing to put your chips at risk to give yourself a stack that can lead to a win. If you pick up a hand like J-9 or Ace-rag and it looks like someone might be pushing you around, take a stand. Put your chips in the middle. You don't want to be anteing off your chips, limping up into second and then not winning.
In these structures, the initial goal is always to cash. Once you've cashed, the goal is to go for the win.