I thought I might have absorbed the difference between “may” and “might” after reading “I Wish I May, I Wish I Might” in Grammar Girl’s Quick and Dirty Tips (a similar explanation is on the Grammar Girl blog). Grammar Girl, AKA Mignon Fogarty, wrote “If something is likely to happen, use may.” Might is for cases when the thing is “a mighty stretch.”
But the next day I read “Mighty Likely” by Jan Freeman in The Boston Globe. Freeman uncovered disagreement among usage mavens about which word is more optimistic. In her opinion, this distinction doesn’t matter much. It may be much ado about nothing.
However, cautioned Freeman, it is important to use “might” rather than “may” when discussing past events.
For another perspective on this dispute, read “May, Might, Muddle” on The New York Times‘ “Times Topics” blog. It may help. Then again, it might not.