Latest news I saw is that Mercedes will own 75% and Ross Brawn/Nick Fry 25% (-ish in both numbers) and Brawn/Fry will continue as Principle/CEO respectively.
Button will have 1 on his car wherever he races. If he's at McLaren, then he's 1 and Hamilton is 2, and Brawn will have 3 and 4. Not sure what they'll do with Toyota's and BMW's numbers as they finished 5th and 6th respectively.
Mercedes are supporting Rosberg, so he is expected to be at Brawn. Nick Fry says they have no need for two German drivers, suggesting Heidfeld may not be in the frame. No mention of Button at Brawn, so probably going to turn up a McLaren.
With no refuelling, and Button's renowned smooth touch on the tiller, he should race well. Needs to recover his qualifying expertise from earlier this season, as a start from mid-grid can't be recovered in the pit stops. But part of me says that Hamilton may hand him his arse on a plate...
Alonso is joining a weak Ferrari, who don't have anyone left who knows how to win. He'll be there if the car's OK, but judging from this year's offering, it might bark a lot!!
As everyone says, another good year in prospect.