We just reported that Apple made available firmware 3.1.3 , but if you are using a jailbroken/unlocked iDevice , DO NOT update ( we are serious. NONE of the tools work with the new FW ). If you are a developer on the other hand, it is time to update your SDK , because Apple just released iPhone SDK 3.1.3.
The new SDK contains the usual Xcode, iPhone simulator, and various tools for developing applications for iPhone and iPod touch. If you want to develop for the iPad instead, you will need to join a $99/year program and download SDK 3.2