Amazon has just hooked up with Facebook to add social shopping features powered by the shopper's Facebook friends list. (NY Times article. WSJ article.) My guess is that this will prove to be the watershed moment for social commerce.
Where Amazon leads, others follow. Amazon pioneered customer ratings and reviews, which are now found on commerce sites across the web.
Amazon pioneered community cross-sell tools ("customers who looked at this also looked at that", "customers who bought this also bought that"), which are now provided to online merchants by at least half a dozen vendors.
And while Amazon may not have pioneered the integration of 3rd-party social graphs into online stores (we've been at this for a few years), the ecommerce world is likely to take its cues from Amazon in this area, too.
Here's what it looks like on my Amazon profile page:
And this is just their initial feature set; lots more must be just around the corner. Merchants interested in the potential of "on-site social commerce" should check out what Amazon has done here and keep an eye on where they go next.
(For those interested in archeology: before Facebook built the one-social-graph-to-rule-them-all, Amazon had social-graph-building aspirations of their own. They called it "Amazon Friends and Interesting People." Dig here to learn more.)