If I'm Shaq, I'm happy with the trade.
Not only has Shaq had problems with Eddie Jones (who seems to always fade in crunch time) stemming from their Laker days, but this trade does a few things for the team.
First, it provides them with more of a fastbreak threat. A Shaq rebound and a deep outlet could lead to a lot of easy scores with Williams, Wade, Posey or Walker and Haslem running the floor. If the transition defense is there, they wait for O'Neal to jog downcourt and dump it into him to start the halfcourt set.
Secondly, Walker can help with rebounding duties, ESPECIALLY if the Heat are serious about playing him at the three. Shaq has never been a fundamental rebounder and now, sapped of his explosiveness, his numbers are going to continue to decline. The help on the boards is needes.
Also, three point shooting is a post players best friend. As long as Williams and Walker buy into Shaq as the alpha dog, they can deter or punish double teams against O'Neal.
Finally, both are good passers and Williams has become an excellent post entry passer. Shaq will get the ball plenty, and in the right spots.
The only reason I could see Shaq being upset with this move is that it will mean he has to assume more of the defensive responsibilities. Williams has improved, but he still has too many defensive shortcomings/lapses. Then again, Damon Jones is/was a matador so that's not much of a change. Walker is a decent defender but will have trouble if asked to guard quick SFs.
Apropos of nothing, I have always had a question about Jason Williams. Why on earth doesn't that guy take it strong to the hoop on a regular basis? He can blow by almost anybody guarding him, and he is a decent finisher or passer when he attacks the rim, so I don't understand. Maybe we'll see more of that under SVG/Riley. Or maybe they'll be content to let him float around the arc on offense. It will be interesting to see how this experiment turns out.