Jeff Bullas posted an interesting article, wondering if Facebook is cannibalizing companies' web pages. I think he's dead right. It's true that whenever you go on Facebook, one of your friends has "liked" this brand or that brand. I tend to "like" people as opposed to brands: Tim Gunn (he's very wise), Barack Obama, the late (and brilliant) Manning Marable, a former professor of mine at Columbia and prolific author who passed away this spring.
With retail brands, I think there's less of a concern. You can't buy products on Facebook; if I want to replace my Carol's Daughter Hair Balm, I'll either look on the Carol's Daughter website or on Amazon. And if I went to a company's website and it redirected me to Facebook, I'd be put off if it didn't have a site of its own. As Bullas says, Facebook owns the content you post on it - if a company has its own site and social media, it can control the content. Likewise, a brand that doesn't make use of social media may find itself behind. Social media builds awareness.
So the key is to juxtapose social media and the company's own content - to use one to drive to the other. You can use Facebook and Twitter to drive people to the company or brand's website by inserting links and running promotions on social media that refer the user to the site. Look at social networking as a supplement, rather than a replacement for the company website - make the goal to be to drive people to the website and increase brand awareness.