I wear black tights for warmth. I wear sheer black hose because I love how it makes my legs look.
Black sheer hose is featured frequently in Vogue, Italian Vogue, and Paris Vogue. When I went to London in December 2011, the trend was to wear sheer black hose, and sheer patterned black hose with shorts(!), boots, and warm sweaters and jackets. Ages 16-I dunno, early 40's. I guess they're used to it (but I thought it was INSANE. It was COLD there).
And Duchess Kate wears sheer black hose sometimes, albeit not with the same regularity of sheer nude hose or opaque tights. So I kind of figure if the royal house of England wears them, and they are featured in couture spreads, you're probably going to look just fine :)