Improve Your 3GS Battery Life

Recently I was dissapointed with the battery life of my iPhone 3GS. When I first got it I was getting over twice the running time of my original 3G. What could be causing this?
Eventualy I remembered that I had turned on the “find my phone” feature under MobileMe. This seems to be the culprit.
Battery life is much better now the setting is off.