Hello,
I've finished the first version (0.0.1). You can download from:
http://pinux.info/calibre/mendeley-0.0.1.zip.
Could someone give a test (I've already tried on Linux, Windows and Mac, but you know...) and let me know if it works?.
It will download the documents in your "calibre" folder from Mendeley and tag as "Mendeley". If you move documents using Mendeley Desktop please remind to press "Sync" (perhaps I should add a warning).