For ordering, keeping track of my plants, in forums, and that sort of thing, I use Latin. If I am talking to someone, likely common, just for the pronouncibility (spell check doesn't like that, hope you get the idea.)
I read this yesterday about the Sky Blue Aster and had to chuckle.
http://garden.org/thread/view_...
In a forum I mentioned I have Bee Balm, and someone asks me which one... Monarda fistulosa. Most Latin names, I copy/paste, but that one I can type up without looking. I can do a few others, as well, only because I referenced them so much.
Common names have gotten me too many times, not only bringing home the wrong thing, but uploading photos to the wrong plant.