The world would be in chaos... The movie 'Bruce Almighty' touches briefly on this idea... In the movie Bruce decides that all prayers should automatically be granted - Effectively granting a free wish to anyone who asked.
Several things happened, but the one that stuck in my mind the most was that a million people prayed to win the lottery, and they all did.
After winning they each got $17.
Many of them were frustrated and angry because their prayer got answered and they didn't get what they really want.
I think most people would waste their wishes asking for things that they think would make them happy but really wouldn't.