Hey Trix,
Glad to hear things worked out for you. That is a tremendous relief I'm sure. I'm really happy for you.
Yes, I am very cautious especially with someones else's data and there is no back-up/fall-back. When working on someones computer, I always start by cloning the drive, and then often I make a separate copy of files.
You state that this is the most problems you have had in 20 years, shows Mac OSX is very robust stable, and the fact that installing a new OS repaired your problems is further proof to that. Most of the time "It Just Works". M$, nah!
Glad installing Lion worked, think you will like it. Has some extra features related to FCPX.
I agree that eventually, your Mac will defrag itself.
Huh, just had spellcheck change defrag to defray, HaHa. You can control click (rt click) to add to dictionary.
Your drive most likely fragged while so very full. Video work writes lots of large files, and when applying effects etc... this adds up. With a slower drive, limited ram, and some weird software glitch, fragmentation can occur. Now that you have some room, Mac will start to consolidate the files.
Apple has a knowledge base article somewhere, and I believe they at the end mention dedicated defray programs may help in extreme cases. I'd just wait.
If you want to run the daily, weekly, monthly routines, Onyx (free) will do it under a GUI. A nice program tool, not toy. Gives user control and ability to monitor process. Lots of other routines gathered together in one place. No terminal for user required. Actually when you installed Lion, part of installation runs these anyway.
You can access Lion Recovery partition by holding down the command key + R key during a startup or restart. It is there to help rebuild if needed. Think of it as a emergency repair service. It allows access to disk utilities, terminal, reset password, and several other programs.
Great to hear your problems solved, enjoy!
p.s. Please back-up HD ASAP!