After a long effort, I've finally released the first version of a dedicated Go Problems app for iPhone and iPad:https://itunes.apple.com/WebObjects/MZS ... 78548&mt=8
It comes with over 200 free problems, and has more problems available for in-app purchase. I've picked through only the best problems on this site, so right now there are about 4700 in the app.
Please check it out, and give me feedback. I want to continue to improve it.