This is, on the surface, an odd move by Button.
Looking a bit further, to some of the recent quotes coming out of the Brawn/Mercedes camp, it seems there are some peculiar forces at work here. And by 'peculiar forces', I mean Mercedes.
Let's take Nick Fry - a seemingly pleasant and intelligent guy - for his word here that
" [ I ] don't think that it was a financial issue whatsoever."
If this deal is not financially motivated from Button's side, why then has he left? Is Nick Fry somehow intimating there were other factors involved? Namely, the influence of Mercedes? From where I'm standing, that seems to be the issue here, about some level of involvement from Mercedes that perhaps did not go down well in the Button camp. Granted, you can argue that by jumping ship to McLaren he's still sleeping with the devil - albeit one with it's horns sanded.
When asked directly about Mercedes and their apparent lack of desire to keep Button, he says
"Mercedes-Benz have purchased our team but they want the team to continue to be run as it has been ... Ross will be the person who makes the principle recommendation."
Not exactly a seal of ratification, is it?
I wonder whether perhaps Mercedes' long term ambition has hindered the short term goal of keeping Button at the team. It's accepted that if successful, the logical star driver in their sights is Sebastian Vettel. By tying Button down to a new, rather expensive contract they may have felt their goal of having Vettel in the team by 2011 would be tarnished somewhat. With Rosberg in tow, perhaps they felt the more sensible option would be to let Button go with the long term view to having Rosberg and Vettel as their preferred driver line up for 2011.
And if this is the case - and admittedly, this is purely based on the inner workings of my imagination - then surely the plan would be perfect right now? Bringing in Heidfeld or Raikkonen for a 1 year deal could be a sensible option while they wait to make their move for Vettel.
But this theory doesn't explain the poorly judged comments from Fry, including this gem
"... I think Jenson is going to have to up his game"
Which can lead you to another theory here - were Brawn slightly disappointed in Button's results? Did they feel the car had more to offer during the times when Button struggled?
It's an almost endlessly fascinating example of team, corporate and racing driver dynamics in which egos and opinions collide to form a kind of political whirlwind.
I'd just like to quickly offer what I think will happen next year regarding Button's move. I come back to the first line of this post - this is an odd move. Button's not known to make bold, successful career moves, but this could be one - depending on how big you want your yardstick to be. If he beats Hamilton over the course of a season, he will undeniably have made a huge impact on the sport and will have shifted people's opinions on him to an almost unimaginable level.
If he gets close to Hamilton, he will suffer the mocking taunt of a British media compelled by this story, eager to find out which of the two is better, but he will not shape opinions, and will largely go down as an average driver who found himself in a great car circa 2009.
If, however, Hamilton trounces him, it's hard to see Button ever being a McLaren driver for too long, and the next lamb will stand up for slaughter at the Hamilton butchery. In this scenario, he'll go down as an overrated driver who made the wrong career moves under poor advice.
I can't wait for the next season to come - it'll be great.
My prediction? Option #2, please.