Bird In The Hand
Within reason, go for the guaranteed than the possibility. As Go (like Chess) has nothing to do with chance, reading out the play to its conclusion counts as the bird in hand. Playing for hope of a misplay is the two in the bush.
A good example would be Black splitting White into two one-eyed groups where either one can definitely be killed, but attempting to kill both leaves bad aji that might allow both to live. If Black can read out how to kill both groups he should do so (unless that in itself leaves him weaker)
This could be applied to many ko threats as one must consider what will be lost versus what can be gained.
Bill: I think that the bird in hand philosophy, as it is usually applied to go, is generally detrimental. It places too much emphasis on territory, not enough on influence. It focuses too much on the local position, at the expense of playing the whole board.
Fhayashi: I agree. Resisting the urge to make a capture that has no further effect on the rest of the board was an important concept for me to learn. I think the proper thinking in the above example is, after black splitting white into two one-eyed groups, using the attack on both white groups to build territory without necessarily killing either group, and maybe even maintain sente.
drgoplayer? So go for the 2 in the bushes if they are a lot bigger than the one in hand (especially if you are behind). In other words just use your head.