I try to stick to the rule "no dot zeros"; last time I had to use a 'dot zero' it was for the development environment for iOS applications. Polite words cannot describe how absurdly horrible that application was; there is no platinum white pill you can take in quantity to make up for that application's release: undoubtably the worse I've used in my career.
I only used the seed release of iOS 5 to test my application that was being released the same day. Mostly worked correctly except a couple dialogs that iOS5 decided were best viewed full screen. Not sure if they fixed that bug before release; assuming not.