I guess Adobe skipping the usual beta release is the culprit.
I have a pretty standard Win7 x64 set-up.
1) After updating ADC to 9.0, LR no longer "Edit in... Photoshop.) It will launch PS if not open, but does not ask or render a TIFF to send to it. I could get it to render a PSD if I "Edit in PerfectEffects plug-in.
2) Perhaps the new GPU rendering? But with a brush, or scrolling or zooming in the Dev Module, the image redraws weird. Sharp, then blurred out. Then comes into focus. Scrolling with my mouses wheel is very laggy and jumpy. (I'm on the latest Nvidia driver for my card)
3) I'm not seeing much i any speed bust.
HDR and Pano are nice, and well implemented.
The brush tool within the Grad or radial toll is nice but not intuitive. You have to invoke it, then go down and click on ERASE.