I've been reading a lot of reviews about the new processors, including the DIY7 article, and decided that I needed an upgrade and bought a new Core i7-920 based machine with 12 GB of RAM. After loading CS4 and capturing some Sony HDV video, I noted the same pixel crawling phenomenon I had noticed with CS2. This seems to be due to a field order problem. The video cleared up when I flipped the field order, which then forced a render on everything, slowing everything down.
I then tried the trial version of Cineform Neo Scene, which cured all the video quality problems I had seen previously. I could also edit the video in realtime without rendering. Neo Scene's capture utility was also smart enough to be able to do automatic scene splitting, which CS4 couldn't do. I highly recommend Cineform when editing HD video. (I'm now a licensed Cineform user.)
Performance-wise, the new system screams. I can transcode to MPEG2 for Blu-Ray authoring faster than realtime. The windows task manager performance CPU usage shows 80+% utilization on all 8 cores during transcoding.