I've found LR4 slower too, running a 6-core Phenom II, 16GB of RAM and Win 7 x64. I'm hoping it's only temporary. I found the same was true with, I believe, LR2. But then, we had to wait for LR3 for that to be rectified! That said, I find it slower, too, in terms of my use. The new sliders are less intuitive that the old one. For instance, Highlights and Whites, do almost the same thing. Shadows I don't find as intuitive as Fill Light. Perhaps it's just me, but I almost didn't get the new version because I hated the sliders so much compared to the old ones.