Like any new service, Snap needs a clear and easily declared vision which defines it as different from the rest, and it needs to pay off on that vision.
It strikes me that great new ideas move in this space due to two big factors: one, a core group of passionate users adopt the service, and two, they evangelize that service without compensation - they believe that what they are using is better, and they want to share that with the world. So to launch Snap, I'd focus on that core group of folks - who are they? What makes them unique? This group should emerge in the next few weeks as the service gets banged on. Engage this core group in conversation, surface that conversation in your marketing, help them evangelize your product and define what the vision is. Perhaps make them the center of your marketing efforts - find out where they hang out, and put them in the ads (with this contest, you're doing this to some extent, it seems, but make the effort even more transparent.)
Also, as I wrote on my site, the new service is attempting to break the mold of traditional approaches to search interface, and to search monetization. I'd trade on Bill Gross's unique claim to fame in doing both these things in the past in your messaging - it's happened before (Overture, X1, etc.) and it can/will happen again.
Lastly, while this may not be a big idea, most services really get traction when they gain distribution from a big partner that also believes in the vision of the service. Who might that be?