Do you seriously think there isn't a problem here ? that there's only a few unlucky people people effected ? that all the satisfied buyers are failing to say how good their purchase is ?
No, I'm sure there are some people who have experienced individual slowdowns for a variety of reasons–and those reasons are being investigated. And yes, obviously, the vast majority of users who are NOT having problems don't got to forums to announce they are not having any problems.
The LR product manager has posted an article about the current issues titled Lightroom 4 Hot Issues
. At this point in time, why some people are having severe issues of extended delays when adjusting controls in Develop isn't known. Many/most of the complaints are not really well articulated and only lower the signal to noise ratio...there have been some useful suggestions about how to go about troubleshooting speed issues on the LR Forum. Some report updating the vid card drivers have helped, some report clearing the LR/ACR cache can help, some report importing into a new catalog instead of updating can help. However, the LR engineering team are trying to track down the various issues and address them. That's really all they can do.
But then you're one of Adobe's NDA tied testers aren't you ?
You're asking a question that can't be answered...he can not really either deny nor confirm. That's the nature of an NDA.