I don't think Obama will have much in the way of coattails on the race for Governor here--- both candidates are well-known statewide, and although Gregoire has been up in 3/4 the past polls by 7-8 points West Coast elections tend to be almost as much about the candidate as the party, and it is not inconceivable that this could be another cliffhanger come election night.
It's not inconceivable. But I don't really see anything working in Rossi's favor, other than anger held over from the 2004 election. Gregoire is a competent bureaucrat, the GOP is in the doldrums, Rossi's transportation plan wasn't received as well as expected. He's also kind of annoying his Eastern Washington base (not totally enthused with him even in 2004) by concentrating his focus on the Lake Washington area. I doubt it will lose him a lot of votes or anything, but he probably needs bigger margins there than in 2004 (he underperformed Bush)
He's running into any Washington State Republican's problem -- you have lick the feet of the Seattle suburbs, and the Seattle suburbs don't seem to be interested.