Yo David!
Like you I was running 10.5.8 and FCP 7.0.3 for a long time on my 2009 MBP 17″. No issues and I was happy.
Then I did 2 jobs with my GH1+GH2 and later 2x GH2 cameras using the AVCHD codec and did the post myself. Both jobs had a lot of static shots with people talking in a relatively controlled indoor environment. Both jobs were transcoded using L&T to ProResLT upon ingest.
On the first job only when I got to the color correction did I notice some ugly graininess in the dark greys. I thought I was pushing the codec too far. On the 2nd job I noticed some ugly graininess and strange macro-blocking in the dark blues after ingest! After a lot of experimentation it turned out that QT 7 was the culprit and was creating the macro-blocking. Upgrading to 10.6.8 and continuing with FCP 7.0.3 was fine and the footage looked beautiful, like it had played out of the camera directly on my Dell Supersharp via HDMI in. I didn’t even have to reencode. It was as if there was something in the AVCHD codec that QT 7 could not “compute” and display properly.
It was early in the project and I was under a time deadline, I did a SuperDuper dupe for insurance and installed 10.6.8 on top of my 10.5.8 install on the MBP HD. It ran well but towards the end of the project during CC FCP would crash ca. once a day. At that point my laptop was just overwhelmed with the effects, so I can’t say if it was due to the OS or not. I have recently started to think I should back-up, wipe the drive clean and do a clean install of everything, especially if I want to go to FCPX.
In the end I realized, with new cameras coming out every 5 seconds and new codecs almost as fast I couldn’t expect QT 7 (unsupported) to keep up with a camera newer than the last QT 7 update. That is why you should upgrade as soon as you can. That was 3 months ago for me and I am starting to think to upgrade to Lion already.
Hope it helps.
Phillip Todd
Cinematographer
Philadelphia – NYC – Zurich
https://vimeo.com/philliptodd