Have you migrated your Mac to OS X 10.7 Lion? Don't.
I lost nearly 100 files a couple of nights ago on my Mac Book running OS X 10.71 "Lion". The files had been saved to directories created from within Logic 9.15, and completely disappeared from the drive when I looked for them in the Finder. They were nowhere to be found with the Spotlight search function, and since Lion doesn't ship on bootable media (as all its predecssors have, going back to the early 1990's with System 7), there was no way to run Disk Tools on the drive to attempt to fix whatever sectors had been written to. As a result of checking with Apple Support, which had no answers for how to recover my data, I've been forced to rebuild the laptop with OS X 10.68 Snow Leopard.
Researching this problem, I discovered that Apple knows of a bug with the Auto-Save function, which may be related to this data loss issue. However, sources seem to point to that issue only when saving to drives that are not formatted as HFS+ (the native disk format for OS X). That wasn't the case with my data loss, since my drive is only 2 months old and was formatted with HFS+ in July when I purchased it. It is possible that 10.72 will fix my issue, but since Apple has kept a fairly closed-door policy about announcing bugs and security flaws in their OS, I would not expect this to get much press attention.
Apple's move to Lion has received a great deal of attention in the media, and since it will likely be required for people to use their new iCloud service, I'm more than disappointed to be forced back to a previous version that won't be iCloud-compatible. But in over 25 years of Mac use, I have only experienced unrecoverable data loss in a couple of instances, so I thought it best to warn people of the seriousness of this current flaw.