The wait is over! Apple finally released the final OS 5 version today for end-users. iOS 5 has several new features including a new notification system. (More info here: http://www.apple.com/ios/).
iOS 5 is compatible with the iPhone 3Gs and iPod 3rd generation and above.
As for jailbreak, yes there is a jailbreak available. The bad new is its tethered for now (which means you need to plug your iDevice in your PC each time you want to boot it up, which can be a pain). The untethered jailbreak will probably be released soon. So jailbreakers may want to hold off on upgrading for now.