I really want to upgrade my Lightroom 3.6 to the new 4, but am reluctant to take the risk based on the bad press your product is getting, esp. regarding response times. Please clean up your product and I'll buy it immediately, the features look great.
Why not download the trial, and see for yourself how well it works for you?
Lr4.1/PV2012 rocks! Lr4 is not perfect, but performance on my machine is AOK.
You should realize there are 2 types of issues:
1. Normal slowness (e.g. first switch to develop module before it has been loaded, subsequent switches when image not cached in ram...). - these effect everyone, including Lr3 users.
2. Abnormal slowness (e.g. develop slider lag...) - these only affect some people.
There are some speed improvements I'd like to see Adobe make, but they are the same ones you experience in Lr3.6, and won't ever make it into Lr4. Fingers crossed for Lr5...
The abnormal slowness does not affect all users. Nobody knows exactly what percentage, but if you are one of the lucky ones, it may perform as well as Lr3.6 does, except have all the new technological advantages of the new Lr4.
PS - Lr4 is faster than Lr3.6 at some things too, including plugin execution.