What are Coke, Starbucks and Microsoft Doing Right on Facebook?

Adweek analyzes big brands on Facebook and declares Coca-Cola, Starbucks, Best Buy, Microsoft and Adidas among the winners. All have used Facebook to successfully build a large fan base. But that’s not all. Says writer Brian Morrissey:

“The real trick after any promotions or ad campaigns that lure in fans is keeping them interested with engaging and useful content.”

This is where Facebook marketing gets tricky. I’ve friended several brands and I rarely visit their fan pages–even when I get an item in my news feed. Is there a disconnect between building a fan base and actually marketing to your fans?