I removed the GenericUSBXHCI.kext from S/L/E. Didn't replace it with anything.
Rebuilt with Kext Utility.
Restarted and not had a freeze since. USB 3 and 2 both still work at prescribed speeds, and show as their respective speeds in Apple System Profiler.
Like bamster said!!
seems it WORKED for me with Yosemite 10.10.3
I had various freezes when plugging usb devices (especially external hdd and bluetooth adapter for mouse).. Just removed "GenericUSBXHCI.kext" from /Extensions folder, ran Kext Utility app, reboot the system.. Magic!
Thank you very much bamster!! I've found your post just in time, I was desperate and I was very close to uninstall and install everything from scratch..
*** EDIT ***
I must correct the last post... Unfortunately freezes go ahead... When I plug any usb devices my Hackintosh freezes!
I don't know why.... any ideas??
*** EDIT 2 ***
Maybe found a temporary solution:
once I've removed GenericUSBXHCI.kext, if I launch Kext Utility EACH TIME BEFORE plugging usb devices I've no freezes! Important: after I unplug my usb device if I plan to insert it again I must launch again Kext Utility to have no freezes...
Someone could explain this? Someone having a "long living" solution?
*** EDIT 3 ***
Solved all my USB Freezing problems doing a clean install using Clover. Until now always seems to be fine so I suggest all of you making this change and choose Clover Bootloader