Although I like that dress and would think about wearing something like that for a party I'm not sure that short of a mini skirt is ever appropriate at work. With leggings or thick tights then it would be fine, as you'd get more of a tunic type effect.
The bare legs issue is I think two fold, first that if the person bent over for any reason, or if you were following them upstairs perhaps the dress would pull up very short, showing upper thighs, generally an area considered fairly intimate, only on view in the bedroom or at the beach. Second it's the contrast (assuming pale skin) so the very dark dress brings the legs to the viewer's attention. Long bare legs are sexy, and sexy isn't generally appropriate for the office. This is after all part of the point of the dress's design.
I also agree that how you present yourself at work does affect how you are perceived, if you want to be taken seriously dressing as a sex kitten may not be the best approach.