I've got my app working (but it's very, very, very, very UGLY - I'll work on that later...). It can now retrieve all your trophies, lists your games and if you select one shows you the trophies for that game. Please note that if you tell it to save your email/password then it does so in plain text. (But you can tell it to save just your email, and prompt for your password every time, or save neither.)

On a refresh, it doesn't have to download all the games again, unless the number of acquired trophies for that game have changed, but I intend to change the format of the cached data before I release it properly, so you will have to redownload it all again. (It doesn't take that long for me, but I don't have as many as Mr Xzbit ).