What can I say after Harvey posted?
.....but I'll try to add something useful.
Something I'm experimenting with right now is double or triple mic'ing acoustic and percussion instruments; the catch is, I'm not particularly going for "stereo micing". For example, I might try to get two mic's on an instrument, but use different types of mics, and in different locations and angles. The result is a recording that doesn't "sit" in the middle of the mix, but for what I'm toying with right now (ambient/new age/unclassified) it's fun.
You get more richness from stereo mic'ing, so as Harvey says you want to be cautious using it in a bigger mix, but if you don't have a lot going on sonically add mic's is a great way to add character and richness to a recording.
-Shaz