Well, I thought that iPhone on a Mac would work without issues. Alas, that is not the case.
Yesterday, when trying to sync (wirelessly or wired), I got this annoying error: The iPhone cannot be synced. The required disk cannot be found.
It took me a couple of hours to find the solution on the web. I did find a few solutions, though they required tons of work (search for a problematic app and remove it, etc...).
The simple solution (OS X - Lion) is this - run Disk Utility, select your HD, and click Repair Disk Permissions.
It took half an hour, but solved this issue completely.
Do make sure to back up your machine regularly though. I have no idea if this could actually damage your data.