Wishes in Dungeons & Dragons are one of the most special yet feared parts of the game. They can save the party from certain death, or bring certain death to the greedy with a mis-worded casting of the wish spell.
From my perspective as a DM, the less greedy the player is with their wish the less likely it will screw them on some level.
It's like the commercial where the guy wishes for "a million bucks" only to be surrounded by a numberless amount of deer - if he weren't being so greedy, he wouldn't have gotten the worse interpretation of his wish.
We talk about wishes (and Sal brings up an amazing legalize "wish contract") in the latest episode of the Brainstorm Podcast. If it isn't one of our best episodes it certainly is one of the most entertaining to listen to.
How do you handle wishes in your campaigns? How far do you go in following the literal interpretation of the wish? How often do wishes show up in your campaigns?