In 1994 America Online trailed Compuserve and Prodigy, a third subscription option in how you hooked your modem up to the internet to go cyber surfing. What propelled AOL to global dominance by the end of that decade was their proprietary 'rainman' platform, which enabled partners to build out their anchor stores in the massive online shopping and lifestyle mall AOL became. Time Warner ultimately bought them with Ted Turner saying AOL was better than sex, and with great swathes of society believing that AOL was the internet, and that anything outside the walled garden was dangerous and disreputable.
We know how that worked out: the internet growing at a fantastic rate as broadband made always on connectivity a reality, and the AOL mall suddenly seeming like a very small and rather dated place. The AOL user experience and the ubiquitous CD rom mailers (decorating countless dorm rooms and burning man installations and serving as coffee mug coasters) is a distant memory now, but I believe what's replaced it is Facebook.
The one stop shop logic is very attractive to the casual internet user (the non nerd), the social graph is powerful and fascinating and why bother going outside the walled garden when this is where all your friends are? Location, location, location means the similar proprietary applications model to AOL in the last century also means it makes business sense to build on the solid foundations of Facebook land. It's growing like crazy, is the logic, everyone's on there and the connections are valuable, it's the shiny comprehensible side of the vast internet, just like the shopping mall is the focused safe haven in the vast sprawling city.
Even the proprietary messaging service within Facebook makes contact with the 'outside world' unnecessary. The business world is abuzz with rumors of vast corporations purchasing Facebook, just like Time Warner swooped for AOL. Against this backdrop, it's not surprising how comprehensible 'Facebook for the enterprise' thinking is attractive, and in fact a walled garden approach can work well for the security constraints companies work within.
Imagine if you'd modeled your business collaboration network around an AOL model ten years ago - as some companies did with the portal approach. It's very wise to take the longer view when a fashion driven approach to anything seems to take over the world - Myspace and Friendster where huge a few years ago and it's inevitable Facebook will be superseded.
There is a clear business value in adopting use models from social network services when they serve your specific business needs, but beware the blind adoption model and the fickle fate of fashion...these days an email from an AOL accounts tells the recipient the sender doesn't 'get' the internet...