The CGMiner zombie thing requiring a full reboot of your system applies to the thumbs too as well as BES hardware.
With the Drillbit Thumbs running I occasionally leave the house to come back to find exactly 50% (1/2) of both my Thumbs and BES' have zombie'd and require a reboot.

This is on Windows, I haven't managed to test them for a long period on MinePeon or anything like that yet, so I expect it to be more a USB/driver issue than hardware fault (Though I'm neither a hardware or software engineer, thats just how it seems to me with the reboot fixing it, power cycling /replugging the devices doesn't so its definitely my PC thats effected by it)