Mine hangs if I exit the app but leave it running in the background, then reopen it later. I think its an issue with how it tried to re-sync after being backgrounded.
If you're on iOS4, that's the likely cause. Don't reinstall, but just double tap the home button to bring up the running apps in the bottom, then press and hold till they come moveable/deletable - and quit the Haypi app.
Launch it fresh, and it should be ok
Alliance : Monti
Alliance : Demented