Jackie,
I'm not sure if you (and The Guinness BoR) use the expression differently from the one I know, or if I'm just missing the joke in the advertising campaign. I'm familiar with something being "the bee's knees" if it's the best. I'll concede it seems a really odd compliment, but I don't associate it in any way with size, per se. We'd use the expression "a bee's dick" (ruder form of "a bee's whisker" which is also used) for something tiny, often in the sense of a small margin ("he missed by a bee's dick").
http://www.artistwd.com/joyzine/australia/strine/b.htm Apologies to the AWAD Filth Police for approaching the gutter again, but that expression is fairly common slang here, and not very high on the obscenity scale.
While we're on the subject of insects' knees, I am reminded of the standard yardstick for shortness, as expressed in the phrase "knee-high to a grasshopper".
