I am almost certain this has been mentioned before, but graal should apply a log in, log out system. When you log in you can stay logged in so when you go on next time it stays logged it (same system as now) but now you have the option to log out and log in as someone different.
It would fix account transfers and would benefit people such as me because my iphone lags and crashes like crazy so when my sisters out i can borrow her ipod 4 and have no crashes or lag.