Missed the Mark
Re:"Meanwhile, youngsters are saying that it's boring and no longer a cool place to chat to mates as everybody's mums and dads are also signed up to Facebook"
Zuck made a prescient choice when he chose to make people unable to protect their privacy. At the time, growth was a matter of life or death. Growth and critical mass has been accomplished and they have been slowly making it more possible to protect privacy. However, they need to go to a much more sophisticated and easy to use permission system that gives back users they type of control they would need to, for instance, allow their parents to be 'friends', but not that kind of friend, if you know what I mean.
I am surprised that facebook has not moved quickly to capitalize on consolidating network effects. They should, by now, be able to target ads so well that they practically only ever serve an ad that is both unobtrusive and effective.
Microsoft has provided a template for 'embrace and extend' and facebook should be all over that. Twitter functionality can easily be put into facebook as can blogging, forums, snapchat, etc. They should offer outrageous stock deals to lure away the very best talent for two reasons:
1) It strengthens them and their product
2) It weakens their competitors and their product.
Now that they have the numbers, facebook should be looking toward the endgame where they truly partner with and empower users such that users have entire control over their facebook presence and associated data and so that users can start to develop anonymous identities and communities. Doing this will make it impossible for governments or other competitors to step into the breach because no breach will exist.
Facebook has the audience to put up a catalog of products people are buying anyway. They have the funds and the reach to cut a deal with UPS similar to Amazon. Because any revenue from such an activity is just 'gravy', they can afford to buy for the maximum price breaks and only offer things at margins so small that even companies like Amazon have no way to compete.
Facebook right now has the very hardest thing to acquire: a relationship with an audience of engaged users. As they are discovering themselves, even with this enormous advantage, it is hard to even keep the audience. Relationship is everything and they have an insuperable advantage right now, but it will melt away like myspace did if they do not fight to keep it. They appear to have been coasting and that is the very worst thing they can do.