I actually think its a good thing... there is no doubt they have cost him the title this season. His relationship is strained and without doubt when you are somewhere for so long the comfort level sets it.
He is without doubt one of the three best drivers out there and wants a fresh challenge. He knows that they will build a car to suit him at Mercedes, where as at Mclaren the driving styles of JB & LH are very different. Does this make it hard for them to provide virtually 2 different cars on a weekly basis?? Lets face it, they havent exaclty tried very hard to stop him leaving.
Sometimes change is good... sometimes its not so good. But credit to the guy for sticking to his guns and trying something new. With hard work it should pay off for him... and if it doesnt.. well he still gets paid a sh1t load gets to go home and bang dat pussy cat doll