The reason Fahrenheit 9/11 was such a big hit (despite being a total mess of a movie, IMO) is that such a full-throated condemnation of Bush was pretty much absent from the mainstream at the time. It was a different story in the latter years of his second term, but between 9/11 and the fall of 2005 you had a hard time finding any true vitriol against Bush outside the lefty blogosphere.
I’ve written about it before here, but two things in 2005 made it OK to hate on Bush in public: Cindy Sheehan’s campaign against the war and Hurricane Katrina. Consider Sheehan–she was just a mother of a fallen soldier who spoke out passionately against the war and Bush’s handling of it. The mainstream couldn’t dismiss her as a dirty unpatriotic hippie, which is pretty much what had happened to any anti-war voice up to that point. She shouldn’t have been such a big deal, but she was. (She also turned out to be pretty nutty, but you can’t deny the effect she had.)
Also consider moveon.org and their infamous video contest. In 2004 they had invited users to submit videos to their web site, and out of thousands of entries, two of the videos compared Bush to Hitler. The videos were quickly taken down, but that didn’t keep the right from losing their shit about it. This was such an uncommon thing that it was big news for a while.
You heard plenty of people saying mean things about Bush if you were really plugged into the blogs or to boards like this one. But you just can’t compare the vitriol that the average person heard against Bush for most of his presidency to what he hears against Obama.