The larger question: All platforms seem to eventually converge on icons to some extent. What I see here is that the concept of sharing is new, and I don't think that's limited to computer uses. We live in a very competitive world where we consume, buy, compete. Sure we share things, but we discriminate in the physical world. I think the notion of sharing non discriminately with ALL our connections is fundamentally new and this is contributing to the lack of a standard symbol.