I won't let out what happens because some people like to be surprised. However, we were there in September and we heard three people ask for ketchup and NOTHING happened. It is hit or miss with your server.
It works better when you have kids probably. DS3 asked for ketchup only because he saw what happened when everyone else asked for ketchup. He thought it was great! I've never seen anyone disappointed when asking for ketchup.
SPOILER:
Everyone in the restaurant that has ketchup is "supposed" to bring it to your table totally overcrowding your table. Then when someone else needs it the favor is returned (with the help of children sitting nearby your table).