[Update: There is a solution for this problem described in this post. The firmware update is fine, but NewerTech's instructions were just a little incomplete. I'll leave the rest of this here to document the problem and the process.]
Drive docks, a relatively new innovation, that let you slot a bare SATA disk drive into a dock that looks like a toaster and immediately begin using the drive, without need for a permanent enclosure, are popular amongst the technorati for many good reasons. They're effortless to use, they avoid duplication of expensive enclosures, and the best of them are highly flexible, allowing you to use any of several connection types (USB, Firewire 400, Firewire 800, and e-SATA).
However, two of what should be the best of these—the NewerTech Voyager Q and the Vantec NexStar NST-D100UFS—were released with the exact same embedded GUID (0x30E002E0454647). This GUID needs to be unique for each device, or else both Macintosh and Windows machines will barf as soon as two of them are connected. The problem with the NewerTech docks was noticed and diagnosed as resulting from the non-unique GUIDs over on hivelogic. I discovered the same GUID lurking in the Vantec docks. NewerTech / MacSales.com / Other World Computing responded on hivelogic with an announcement of a firmware update that would fix the problem. I contacted email@example.com, per their instructions, downloaded the firmware updater at the URL they provided, had to use a Windows box to do the update (Grrrr!), only to discover that the update doesn't help in the least.
The update doesn't seem to hurt the drive dock, but it doesn't change the GUID and it doesn't allow two units to be attached to the same computer by Firewire, either in parallel or daisy-chained. The email I received from MacSales Customer Service with the link to the update stated that "it will assign a unique ID to each unit". But it doesn't. I followed the instructions carefully. The firmware uploader tool reported success. Scanning the unit a second time reports V1_20 instead of V1_10. Attaching it to a Mac, System Profiler reports 0x120 instead of 0x110. It's clear that the upload worked and the firmware was updated. But the GUID is the same problematic 0x30E002E0454647 in every unit. And the problem with instant, error-producing dismounts when attaching two units is unchanged, whether the units are attached to two different Firewire ports or they are daisy-chained into one. (In fact, now the Mac has to be rebooted before even a single drive can be seen and mounted, after one of these conflict events; I don't believe that was the case previously.)
Unless NewerTech or Vantec provides a solution for this, my only recourse is to return the units for a refund. Grrrr!