My 8 board has lost USB connection with the Linux box 4 times now, stopping and starting cgminer 3.8.4 doesn't help, I have to reboot the linux box each time.
Others with this problem as well:
http://drillbitsystem.com/forum/index.php?topic=184.msg1619#msg1619Reverting to 3.8.1 seems to have fixed it.
Not getting this problem with my boards on Windows 7.