I saw it.
My thoughts:
I thought Josh Brolin was great and most of the pleasures of the film is that of watching how the impressions played out. Some were good, like Thandie Newton and Jeffrey Wright, and were not so hot, like Richard Dreyfuss and James Cromwell, who were too themselves to be convincingly someone so well known.
If you are curious to watch it just to see a disaster, you'd be better off not going. There was one disasterously bad scene (one of them being an attempt to re-create a CNN/Fox News type show that they titled 'Spin Ball') and very crowbarred-in Bushisms, but for the most part it was an okay movie. I didn't dislike it, but there are enough times where you just go 'whats the point of this movie'. It was very sympathetic to Colin Powell and somewhat sympathetic to George W. Bush, while being the opposite to Cheney, Rumsfield and others. It takes place entirely before 2004 which I found disappointing since pre-04 Bush made some sense where as post-04 Bush, it feels sometimes like he doesn't exist.