We have been using Keyspan USA-19HS USB to serial converters for about three years with both Mac OS X and Windows applications, with Windows provided by Virtual PC and now through Parallels. In the past month 4 of the 5 have stopped working. All failed while connecting/disconnecting from a Mac Book while running Windows XP via Parallels (build 3214). The converters no longer work with native Mac OS X applications either. The LED no longer comes on when plugging into any computer. I called Keyspan and their official response is that they do not support using their products with any virtual machine. The failures that occurred are the same for all four: the firmware was erased or corrupted. I am now waiting for a response from Keyspan to get the firmware reprogrammed by them, though I suspect that would cost more than buying new ones. So, the bottom line is use Keyspan converters with Parallels at your own risk. If you know other supported converters, please post them here.