[HPBEggo]

This.

Simply posting something that already exists, be it through a Tweet or a link or what-have-you, does not create anything of value.

However, creating said link with a short description or within the context of a greater article does create value. It's not a huge amount of value, but I know that I, personally, am much more likely to examine a link posted by someone if they explain what it is about and that explanation is both interesting and relevant.