iPhone 3G third party applications crashing on startup
Sometimes third party applications (like Monkey Ball) will crash and return to the home screen after loading for only a few seconds. This problem appears to be related to an incomplete AppStore download. Rebooting the iPhone is often all that's required to fix the problem. If rebooting fails to work then loading up the App Store on the iPhone and downloading a free application or updating an existing one will almost always fix the problem. The last resort would be to do a full sync/backup with iTunes.
I've never had to restore the iPhone firmware to fix this problem as one of the three previously mentioned problems will fix the issue.