This is a big risk for LA. We're talking about Ron Artest, here. The dude is not stable. Throw him into that drama-filled environment with the LA media fishbowl, and anything can happen. You up the pressure on Artest and bad things have a tendency to happen.
Not to mention the fact that he isn't the defender he used to be and can be a huge chucker on a team where Kobe gets all the shots. And Kobe is a ty teammate and domineering personality... this has all the potential of a gigantic trainwreck. Ariza is 6 years younger, doesn't demand the ball, and only getting better.
This is highly volatile. I don't understand why the Lakers take this gamble. It seems highly unnecessary when the Spurs can't keep Duncan and Ginobili healthy for the playoffs and they don't have any other real compe ion in the West.