Procter & Gamble is doing it. So are retail giant Walmart, jeans manufacturer Levi Strauss, Malaysia Airlines and UK cinema chain Odeon. Even Lady Gaga is a fan.

They’re all establishing online stores on Facebook, using the social networking site as a platform for attracting and processing sales. In some cases, orders are re-routed in the final stages to the shopkeeper’s own ecommerce site — but in many others, they can be conducted entirely on Facebook.

Brands are diving into so-called “f-commerce” for two reasons: to reach the widest pool of customers by setting up shop where the customers are; and to turn those customers into valuable advocates 
for their brand by sharing information about their purchases with their friends.

The trend began around two years ago, but has only recently started to gain momentum. Several obstacles still exist, however — a major one being consumer attitudes. In a 2011 survey of US and UK consumers conducted by research firm JWT Intelligence, almost 80% said they worry about the privacy implications of shopping on Facebook, while three-quarters said they “don’t think Facebook is secure enough to make purchases on.”

Web marketers, meanwhile, worry that the Facebook environment lacks not only the flexibility to tailor the “look and feel” of their stores exactly as they’d like, but also the integration capabilities needed to tie the data collected there into their primary ecommerce systems.

However, Facebook is working hard and fast to improve its commerce capabilities. What’s more, few brands will want to limit online transactions to a single digital destination, their “official” ecommerce site: Facebook’s 800 million-plus users are, quite simply, too big a market to ignore.