Same problem. I think it just started about a week ago.
I have ICLOUD email/calendar on my PCs, one 5th Gen iTouch, one iPad 2, one iPad 1, and one iPhone 5
I can enter a calendar entry on one of my iPads' and it will sync with the other iPad but not to any of my other devices or PC calendar.
My suspicion is that is somehow due to this business of having to have an icloud account?
I am not sure anymore if I am a @me.com or I am a @icloud.com and if that has something to do with it?