I had Vista installed on a with 2GB RAM without any noticeable performance problems, starting with Beta 2, despite everyone I came across on the Internet telling me you need at least 3GB RAM to run it well. Now I have Windows 7 installed on the same computer and I can't tell much of a difference.
I'm sure there are people who ran across problems in their installs, but every release of Windows since Windows 95 has been met with a lot of cynicism from people who dislike Microsoft and spread FUD. I remember when Windows 95 came out all I would read about it was horror stories about people having installations problem. Meanwhile, I was able to install 95 on about a dozen computers without a problem on any one of them. Windows XP when it came out was a very hated OS, but now everyone is calling it the best OS that Microsoft made.
People need to realize that some of the negative feelings about Microsoft products is not their fault. It's that simple. Vista had some problems with its release, sure; I've been a critic of Vista also. But unless a Windows release is flawless and perfect people will badmouth it.