In direct answer to your question: just launch. In response to your app itself: I would suggest offering arbitrary thumbnail sizes( not just 72px ), up to an

In direct answer to your question: just launch. In response to your app itself: I would suggest offering arbitrary thumbnail sizes( not just 72px ), up to and including full-screen resolution. In addition, I would suggest a snapshot scheduling service, such that regular images are captured for given urls on a regular schedule. A company like us, for instance would probably pay for a service that allows us to build a design history of our web properties automatically, instead of adding "screenshot the existing live site before deployment" to the design or technical workflow, or relying on the Wayback Machine to do so.