The problem right now is that you need to go outside the sandbox in order to make a web app feel first class. Chrome has solved it with a modal/dialog that ask

The problem right now is that you need to go outside the sandbox in order to make a web app feel first class. Chrome has solved it with a modal/dialog that ask users to add the app to the home screen, but I think the modal/dialog in Chrome is too spammy. It's better if users can do it manually, but its currently hidden too deep in the Safari UI, and Im not even sure you can reach it in mobile safari UI.