I just found out that the term "Social Commerce" was coined by Mary Ruddy in a conversation with Paul Trevithick. Mary first used the term publicly in a podcast from IIW 2005.

Since, Yahoo picked up the term, assorted startups use it and many people blog about it all the time as it seems.

Score one for Paul and Mary for anticipating yet another important new trend … currently, they are most visible as leading the Higgins digital identity open-source project to which they have attracted heavyweights IBM, Novell and others.