I've got a 32GB exFAT-formatted USB drive that I use for shuttling files between work (Win7 PC) and home (Macbook Pro Retina). I up'd to Yosemite like many others after IOS8 also dropped, and didn't have any noticeable issues; until I tried plugging in my USB flash drive. It's completely invisible to my Mac. It doesn't auto-mount, it doesn't even show up in Disk Utility for diagnosis. It still loads fine on my work-PC (no surprise), but here's the kicker - It still mounts perfectly on my wife's Macbook on Mavericks. I plugged it into my wife's Macbook and it popped right up, copied over a file as a test, then ejected it properly and tried re-mounting on my MacbookPro; still not loading. Help please!? I've Googled this over and over and got nothing. What am I missing?