With the help of DressRegistry.com:

Our goal is to lessen the chance that someone attending the same event as you will be wearing the EXACT same dress. We also hope we can be a resource for groups planning events through our message board and marketing partners. While it’s true we can not guarantee that someone else won’t appear in the same dress as you, the more that you (and others like you) use DressRegistry.com the lower that likelihood will be. So please use our site and have fun!

You find your event on their site and post a description and picture of the dress you will be wearing.  When other guests check in to the site, they will know which dresses to avoid, in order to prevent dress disasters such as this one (Pink and Shakira, featured on the site):

The site promises “No personal information is displayed” but I wonder if anonymity is a desirable feature in this kind of mechanism.  It seems to open the door to all kinds of manipulation:

  1. Chicken.  Suppose you have your heart set on the Cache: green, ankle, strapless (picture here) but you discover that it has already been claimed for the North Carolina Museum of Art Opening Gala.  You could put in a second claim for the same dress.  You are playing Chicken and you hope your rival will back down.  Anonymity means that if she doesn’t and the dress disaster happens, your safe because there’s only she-said she-said.  Worried she might not back down?  Register it 10 times.
  2. Hoarding.  Not sure yet which dress is going to suit you on that day?  Register everything that tickles your fancy, and decide later!
  3. Cornering the Market.  You don’t just want to avoid dress disasters, you want to be the only one wearing your favorite color or your favorite designer or…  Register away all the competition.
  4. Intimidation.  Someone has already registered a knock-out dress that’s out of your price range.  Register it again.  She might think twice before wearing it.