I think that W the movie will suffer from the fact that a lot of times, moviegoers don't want to go see at the cinema what they can see on the news at home. If 80% of the public disapproves of Bush, why would they want to go plunk down the dough to watch a movie about him, regardless of the political slant of said movie? I think the general feel right now is that people are just ready to move Bush off the political scene (much like people tend to feel about any 2nd term president) and won't go sit for 2 hours watching people pretend to be him and his administration.
Had Stone waited 10 years, maybe then, but I just don't see it being wildly popular right now.