Surf some computer boards, going back to 2001/2002, and you'll see very same Vista haters, saying very same thing about XP.
There was adjustment jump from Win 98 to XP, as it's from XP to Vista.
Then, adding to what patio said, I can assure you, most people, who don't like Vista, never used it (saw it on uncle's computer), used it for couple of days, or had it on machines, which didn't meet Vista hardware requirements. The latter are probably most common.
"Oh, man, my Vista is so slow, I hate it..."
"What kind of computer do you have?"
"Oh, 1.5GHz processor, 15GB hard drive, and 512MB of RAM".