Getting Turkoglu back was good. Giving up Carter to do so was even better. Even when you had to throw in Gortat and Pietrus, I still think that will eventually pay dividends.
But the Arenas trade was and remains puzzling. Lewis was WAY overpaid, no one disputes that. But... so is Arenas. So you get more scoring potential, I get that, but more of a head case. Sure, Arenas isn't likely to disappear in the 4th like Lewis did, so I guess that's better. But like Chris said, that's an extra guy who needs the ball in his hands.
If you make another trade, I could see it working. As it stands now, Turkoglu will reestablish himself eventually. But I really don't see Arenas working well.