One thing also to consider is the metagame implications of a call.  I don't think this arises in turbos, SNGs, etc but is something to keep in mind.  A lot of the time in the early stages of tournaments, you will be faced with scenarios where you think you are ahead, but cannot be certain, and will have to make a decision that could lose all of your chips.  In these situations sometimes it is best to wait for a better spot.  For example, let's say it is the first orbit of the WSOP main event and you are dealt QQ.  You raise 4xBB and someone just shoves over the top.  Hypothetically, let's say he shows you AKo, so you know what he has.  Mathematically, it is a fairly easy call if you view the hand in isolation.  You are slightly ahead and there is money in the pot.  However, doubling up will not actually double your chances of making a run in the tournament because there is so much poker left to be played.  Losing the hand will drop your chances of winning to 0%.  So from a metagame perspective it is actually an easy fold.  Not to mention that in this hypothetical, you know what your opponent has, and in reality you wouldn't suspect AK you would suspect AA.  Phil Helmuth even said that he would fold AA in the early stages of a tournament to an all in bet because he would suspect someone else would only be willing to get it all in if he had AA as well, but also because he thinks that the 20% chance of you losing to a set if your opponent had KK, is not worth the 80% of doubling up.  I know that this scenario is very different from the one I'm describing, but the point remains.  Now if you drop your hand value from QQ all the way down to 1010 you can see that it's ok to fold.  Purely from a mathematical perspective, you could call or fold, it's probably close.  But from a metagame perspective, you should probably just fold, especially if you think you have an edge over the field.