Here’s the big grain of salt to accompany this: Twitter is a platform more suited to what currently constitutes advertising and branding. Twitter is (for the most part) a way to consumer information. It breaks news. Facebook is a medium for engaging with and consuming people.
Brands are not people. Brands are a hack for when people aren’t available (which is why they’re so well suited to TV and other media where audiences don’t actively participate–their slight of hand isn’t interrogated by interaction). Until companies figure out that Facebook is a space for people, employees, workers, not the classical idea of a ‘brand’, advertisers will have limited success with Facebook.