So, as a Cavs fan (not just Lebron) I will add a little Cleveland perspective.
Relegating Z to the bench is perfect. Z is a major defensive liability against any team with an interior presence. Just look at how many points in the paint the Cavs gave up against ORL, BOS and LAL. Shaq pretty much takes care of that problem single handedly. Shaq will now command a double team which will help Lebron get free. It will also allow Mo, Delonte and Carter to get open for 3. Anyone who thinks that Shaq will clog the lane obviously didn't watch him play with Kobe and D Wade. Shaq definitely helped them, he didn't hurt them.
Shaq also provides a big finisher in the paint. Think about all the times Lebron got doubled and had NO ONE on the inside to get the ball to so he would kick it out for a 3. Well, now he can draw the double team and dish to Shaq for an inside finish. Much more efficient.
Carter and Moon have the size to guard an outside wing taking some pressure off of the Cavs other smaller guards. In the Orlando example, this would leave Lebron to cover Lewis, LBJ will still cover Pierce against Boston.
As for Lebron leaving next year....never going to happen. He will not take less money to go to a non-playoff team. I actually think he is much more likely to take his player option after next year and wait to see if the cap goes back up in 2011.