Facebook has been around for 8 years, it's one of the most heavily-used web properties in the world. I just had an IPO and nearly a billion people have an account. It's staying power revolves around the web of photos and collective memory that we all now have of the last 8 years.
One day Facebook's usage and magic will peter out. I wouldn't call that a failure. Some will. I think they've had some damn good success up to this point and will continue to for the foreseeable future.
