One type of situation has troubled me when I've faced various versions of it. In the later stages of tournaments where the blinds are significant, I find myself wondering what to do when it comes down to a blind vs. blind situation. I know there are a number of variables, so answers can involve how those variables effect the decision.
I'm particularly interested in playing out of the SB with marginal holdings. This position is odd because it offers the initiative to steal the blinds but is OOP for the rest of the hand. I've often found myself raising preflop with a marginal hand and then not knowing how to proceed once called. I suppose I'm thinking mostly of situations where both of us have relatively small M's, as these hands aren't as interesting if both players have large stacks.
Of course this depends on the type of player, and that knowledge might answer the question. So for this question let us assume that we know little to nothing about the player (tough to read or one of us just moved to the table).