|Facebook's iPhone Apps|
Because so many social networks have bloomed and wilted before Facebook arrived, there seems to be this thought among a lot of people that Facebook too, in the near future, will pass into irrelevance.
Some of the facts.
Every other social network relies on publicity from their feeds appearing on Facebook user's timelines (except maybe twitter, but even they have greatly improved their ability to sync your tweets with your timeline.)
Facebook is to become integrated into the iPhone operating system. Although Android has boasted this feature for ages, iOS users are more active and spend more money online.
Facebook makes money.
Facebook boasts one of the highest regular users rates among its peers. That is to say, not only do they have a lot of people signed up, but a lot of those people actually log on to Facebook regularly.
Facebook owns Instagram, and has enough money now to buy any other serious threat that could pop up.
A lot of telco's (in Australia at least) offer free data for anything Facebook related. This has helped breed a habit among youth (with no jobs) of using Facebook as the primary means of contacting friends.
Some of my opinion.
Facebook has reached a tipping point similar to what Google (search) did, where it is just too large now and used by too many peoplefor a competitor to rally any serious threat.
Facebook has enough features that it could actually release its own phone and you would hardly have to leave a Facebook app... ie messaging, contacts, photo/camera, newsfeed.
Facebook has credibility with a diverse demographic, from 13 year olds (and younger) right through to middle aged people, and reaches both males and females. The fact that it's not just "for kids" means a lot.
Facebook has a very shrewd CEO in Mark Zuckerberg. He owns a controlling stake in the company and thus gets his own way still.
Google+ is a failure.
Twitter is infested with spam.
It's foolish to say it will ALWAYS be number 1. But I hold a strong opinion that it will remain THE social network of the English speaking world for the foreseeable future.