Auto run workflow, upon mounting of USB drive

you can use a launch daemon set to be triggered when you mount a disk.
Use [Lingon|http://lingon.sourceforge.net> for that. If the only disk you ever mount is your USB stick, it's quite straightforward. Just set the launch daemon to run your workflow on disk insertion.

If you also use other disks you'll simply get an error message when you mount something else and your thumb drive is not present. If you don't want to see the error message you can use an apple script. Something along the following lines:

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tell application "Finder"

if exists disk "thumbdrivename" then
tell application "path:to:your:workflow" to launch
end if

end tell

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and set the daemon to run that instead of your workflow.

you are welcome!