I enabled the plugin (so that a crossed-out plug was shown), waited for a moment and plugged the device in: it was detected by Calibre. I repeated this a couple of times, with the same result (I restarted Calibre and switched the plugin on and off).
I'm on Calibre 2.60, Win 7 Pro, the device was Kindle Paperwhite 3. I'll check it again: if it works for all of you and nothing relevant has changed, it should work for me as well
.