I was a wee lad in the "mistake by the lake" when this happened in 1986. I didn't really remember it until I saw this video footage this morning:
Most of the launched balloons came down immediately into Lake Erie, where they hampered the search for two missing boaters. Both boaters were later found dead. Miles away, the descending balloons spooked a prize show horse. Lawsuits were everywhere. A nearby airport was closed down temporarily.
I asked my roommate if something like this could happen again. "No way," she responded. "No way, is right!" I added.
The balloons were launched for charity. Also happening at the same event: Taco Bell created the world's longest burrito (320 feet!), chopped it up, and sold it to raise more money for the United Way.