This reminds me of the problems Color had initially. They launched it worldwide, when a targeted rollout in densely populated tech areas (e.g. SXSW) would have given them a small number of happy users to build from, instead of a larger number of pissed off ones ( http://techcrunch.com/2011/04/29/how-many-mulligans-does-col...). But grooovy hasn't, I assume got $50 million of funding, so you won't get hammered for wasting it. Target the tech-heavy cities, like SF, Boston, London, where lots of people have iPhones and use a lot of apps, and where tech journalists live.