The most social brides are most likely socializing on Facebook, given the social network’s dominance online. So it’s no surprise that The Knot, one of the most recognizable online brands for wedding planning, has acquired one of the most popular wedding Facebook apps Weddingbook. The Knot has actually acquired WedSnap, the development company behind Weddingbook’s Facebook application, with sure hopes of tapping into Facebook’s wedding-specific demographic.

From a high level this seems like a smart acquisition, given The Knot’s inability to make its own destination site wholly integrated with truly social features. The company’s necessity to turn to something like a standalone Facebook application goes to show the trouble even dominant destination sites have with layering in social features, and the power of Facebook’s platform.

As a winner of $250,000 in the fbFund just weeks ago, Weddingbook has a lot of useful features that make the act of wedding planning quite social. From discussion boards, to wedding profiles, wedding updates to wedding countdowns, Weddingbook has it all. And the application taps into the Facebook social graph to help users get things done, like event postings, registry links, photo albums, guest books and the ability to allow other users to offer their input on a variety of wedding-related occurrences. The wedding itself is often quite social, so why can’t the planning process be as well?

Along with The Knot’s other acquisition The Wedding Channel, Weddingbook will be part of The Knot’s rapidly growing network of websites and applications. While I don’t think The Knot will be seeking for ways to incorporate its other acquisition, Breastfeeding.com, into Facebook any time soon, it’s clear that The Knot is really looking to stay on top of the online wedding-planning phenomenon, going the organic social route with the acquisition of Weddingbook. This may be quite a smart move giving the current state of the economy, as many brides (and grooms) may be looking for more cost-efficient ways in which to plan and share aspects of their wedding.

Though Martha Stewart’s brand Living Omnimedia Inc. has made some strategic investments and acquisitions in the past year, none of them have been particularly social in the larger integrated sense. So it will be interesting to see how The Knot takes advantage of its latest acquisition within its own network of sites and services.