I'm hoping that Mark Webber moves to Williams. He's just signed for Jaguar, but he's a wasted talent there. I'm a little biased cause he's an Aussie, but he squeezed a hell of a lot out of the Jag last season (scoring 17 of their 18 points). Webber used to test for Williams and apparently Frank Williams really likes him.
Anyway, to answer your question...I think JPM is a hugely talented driver and has probably been let down by the Williams chasis in the last few seasons.