This is cool, but I find myself ever more concerned about Google's terms of service. I don't seriously expect them to abuse in the sense that they'd use private documents and photos, etc. But Mockups will just be one more thing for which I'll be a granting Google a permanent "worldwide license to use, host, store, reproduce, modify, create derivative works, communicate, publish, publicly perform, publicly display and distribute such content." Legally very difficult to justify going Google.