I actually had a chance to be in that Webinar, and since then I did started implementing stumbleupon, digg delicious and reddit in my posts. I’ve had a good deal of pageviews from Stumbleupon, the traffic appears to be American, so what you are promoting should perhaps have brands that accept US players.
Nevertheless social links are good for any website and even if there was no traffic I would still use those major ones to build links. Just read the article quite informative 