Now check this out. I have a MacBook Pro 15'' 2012 with OS X Mountain Lion 8.2 on one partition and Windows 7 on the other (Boot Camp). I replaced the optical drive with another HDD, in fact I used the original 500GB Macintosh HD as additional HD and installed a new SSD as the main drive. Not knowing what to format the original HDD in, I'd read that exFAT would be compatible with both systems, so I proceeded to format it like that, and then I transferred over 300GB (music and other files) on it, confident that I'd've been able to modify the drive from both W7 and OS X. Today I was playing some of music on the HDD in OS X and all of a sudden the playback became intermittent, as if there was some glitch. I saved the music I wanted to play on the SSD, and it went fine; but then for some reason I had to restart the computer, and upon reboot, surprise surprise, Mountain Lion tells me that there is disk that needs formatting. I'm like, wtf? Well it was the HDD. The partition had become all of a sudden unreadable, so I had to reformat it, thereby losing all the data. Now I am (hopefully) recovering the data with Aidfile, which is still running and smoothly too, but - again - WTF. I seem to have read somewhere that exFAT can cause instability cross-platform problems, but this is epic. Now I am going to reformat with Mac Extended Journaled and to hell with Windows.