They call it, "The Steampunk World's Fair" and it will be held next year in Piscataway, New Jersey, from 20 May to 22 May 2011. The 2010 edition (14-16 May 2010) had attendance of 3000 over its three days. The venue is yet to be announced, but it sounds like it's a go, and it could be cool. Here is a link to their site.
