"I think that sellers' time is usually going to be better spent optimizing for Google Shopping, exporting to Craigslist, or otherwise spending their efforts getting their items optimized for channels explicitly designed for ecommerce."
This has always been my feeling on the idea of social networking.
That would be 1% of my sales since I've had a page there.
I've heard that some people who do heavy marketing have got it a little better, but I can't see spamming all the time! I've hidden the posts of some friends who post too much of their stuff -- and I know that my friends would do that to me. And I think some of the social networking might be better for those with stand-alone websites and a smaller, focused market who already like them on FB. The group most likely to shop that website.
I'm big on using twitter and facebook. But I think how you market is key. A lot of times I try to get my tweets/posts retweeted/shared by ppl with a large following. It's instant exposure and it's how I've been driving a lot of traffic to my shop.
I agree, Cindy, engaging with the audience is important! I know that some e-sellers (like Beth, from blackphoenixalchemylab) get a lot of repeat customers by communicating with them on twitter and facebook and staying on the radar (and just being lovely in general).