One of the great things about GGJ which makes it differnet from other jam events is the big theme reveal after the keynote. It is a really big moment for a lot of the jammers, and many people get excited for the big annoucement.
We try really hard to keep the theme a secret until 5pm in Hawaii, so everyone has the same chance to be excited about the big reveal at their site.
Add in about keeping the theme a secret.
Add a link to the page where you can check if the theme is a secret.
Also remember don't share the theme with anyone external from your site, like people jamming at home. It is much harder to stop them tweeting and sharing.