Essentially, you are Long-Tailing it when you social bookmark. You are delving into smaller and smaller niches.
Not even 50 percent of this planet is online. Fewer buy online. Even fewer (about 20% of those and mostly a younger demographic) social bookmark.
You are not trying to get the "got bucks" boomers. Boomers are still probably best reached through article marketing, opt-in email lists, and so on. Web 2.0 is used to get onto the front pages of Google. But social bookmarkers will get the news from their friends, not necessarily websearches.
That's the mental framework to crack - most first-generation SEO guys probably won't make the jump, as it's a different world-view. However, the brightest (younger) ones are being brought up with this and it won't be that much of a challenge.
So, watch your limits and make sure your product is one which will sell in that climate.