I have FCS 2 installed and, as of today, things are running perfectly fine. The OS is definitely faster, Quicktime seems way more responsive.
Example: on my MacBook Pro 2.4 4 GB connected to a Esata 4big Quadra with a Sonnet Tempo Pro/34 card I opened 2 1080P ProRes HQ Trailers at the same time with no dropped frames at all, something that wouldn’t happen on Quicktime 7, and CPU was around 65%….
Always learning….