Really I think the new Exp. Share is a great tool and Key Item...but it doesn't fit my playstyle. My first playthrough of Y I left it on and my Pokemon were extremely overleveled in the Pokemon League (My Pangoro and Tyrantrum were both in the 80s, and the rest of my party was spread between the 60s and 70s). I think the Exp. Share is useful for a playthrough where you are constantly swapping out your team members, making new parties every few cities because of all the available Pokemon. But if you are using one main party throughout the entire game, I think it makes the game way too easy.
But, now that I've beaten the actual storyline, I did turn it back on. It's very useful for training up multiple Pokemon, like I said, especially thanks to the new EXP system.
While I do miss the old Exp Share, I don't mind this one too much, as long as I am always able to turn it off. :)
The option I chose in the poll was "I turned it back on after the e4"