Definitely a case of PEBKAC, and more people having access to the internet than during XP's launch, thus more people being exposed to the internet echochamber of suck, and taking it as truth.
Also, I get the feeling that there's just a sort of vibe that goes around.. like a zeitgeist kind of thing. At Vista's launch, the vibe was bad, and as such Vista was deemed bad. Now we're hitting the other end of the wave, and Windows 7 is hailed as the
second coming, even though I get the feeling it's not actually that much better than Vista.