The list of essential social sites for brands and retailers grows longer every year. It's like taxation without representation. Facebook, Twitter, YouTube, and a company's own blog are must-dos. Also vying for the attention of a sustained brand presence are Instagram, Pinterest, Tumblr, Flipboard, GetGlue, Polyvore, and potentially dozens of other new startups every year.

With the social media landscape changing every six months, marketers should not be surprised if at least two social sites break through with high traffic and a unique concept every year.

Obviously a brand will find it challenging to create original content for every site in a sustained manner. Brands must pick...