Usability problems with .Mac sync - I can only confirm what Jeffrey Zeldman writes here. Apple's sync tools are simply terrible. I have had the sync of trivial data between my iMac under Leopard and my notebook under Tiger crash multiple times - fortunately, only one is leading, and in an emergency I can simply reset everything. But worse than the sync of simple data (contacts, calendar, etc.) was the sync of the keychain - it took me quite a while to clean up the damage. And the iDisk? Oh man, I only tried to edit 4 OmniOutliner documents on both computers in turn. Result: dreadful. Simply and plainly junk. For documents, I have simply switched back to Mercurial (I use it anyway for my other documents, the outliner files were just a test). It is reliable and stable. Even if it only offers a command line as an interface - for data synchronization, I want stability and not gimmicks. Sync services that crash my data are simply garbage.