A shopping mall in California gave away free gift certificates. They were in balloons that were dropped. The only problem is that 2,000 people showed up for 500 gift certificates. Nine people received minor wounds and an elderly woman went to the hospital as result of the stampede to get the balloons once they were dropped.
Any time the price of a good is 0, you won't have enough to go around and some other way of allocating the good will take place. In this case, people who could move the fastest and knock other people down got the goods.
You can read about this at this site