The UK broadsheet newspaper, The Guardian, has reported that according to estimates reached by the social media marketing and analytics company Socialbakers, Facebook has lost some six million US users in the past month alone while in the UK 1.4 million have deserted that nice young Mr. Zuckerberg's splendid site over the same period. This, it seems equates to a four per cent and four and a half per cent of the audience respectively. It is said that in the States, over the last six months, more than nine million former aficionados have taken their outpourings elsewhere.

Could it be that in many geographies Facebook has peaked and the only way for it is down? Well, it is a possibility now and probably an inevitability in the future. Users of social media sites are a fickle bunch and will churn away to something they perceive to been more fashionable at the drop of a hat - and once a trend gathers momentum it is all but impossible to tell when it will peter out. Remember MySpace?

However, although there are few "new to the world" potential Facebook subscribers left in North America, parts of Europe and the Far East, the site continues to grow in popularity in the still largely untapped South American market and other parts of the world where broadband penetration is either still in its infancy or just beginning to make a serious impact and social networking sites are very much a novelty.

For example, in Brazil, Facebook has recorded a six per cent increase in users over the past month and the total repeat visitor number now stands at 70 million and rising. Uptake is also growing in Argentina, Chile, Uruguay, Mexico, and even Venezuela as well as several other South and Latin American nations.

Elsewhere, user figures in India are up by four per cent in a month with 64 million consumers now making repeat visits to the Facebook site.

However, it is in developed markets where Facebook seems to be in decline both in terms of the defection of users and the amount of time continuing users choose to stay on the site - but that reduction in face-time for Facebook may well be down to the massive uptake and popularity of tablets and other mobile computing devices and the concomitant relative downturn in the use of laptops and desktop computers.

Indications are that Facebook is also shedding users in Australia, Belgium, Canada, Denmark, Finland, France, Italy, Germany, Japan, The Netherlands Portugal, Spain and Sweden.

Facebook's biggest problem now is to increase its mobile user base or face an eventual financial pressure Revenues from mobile advertising are Facebook's Achilles heel and Zuckerberg et al know it.

We'll find out more tomorrow when Facebook is due to provide its next trading performance update. Expect a lot of emphasis on Facebook Home, the Android phone app on which Mark Zuckerberg is pinning a lot of hope.

Of course, all this is relative. Facebook remains a mighty power and presence and analysts are expecting the company to report that revenues have increased by at least a third year-on-year.

So, Facebook is still riding high and can more than compensate for the loss of a few million users. What it has to beware of is that the trickle of defectors doesn't increase to a flood. It's not for nothing that the company is looking worriedly over its shoulder at the likes of Path, a social network designed specifically for mobile devices. Path was designed by one Dave Morin, who used to be a Facebook employee.

He saw and exploited Facebook's weak-spot and understood user frustration with the proliferation of ads and marketing garbage that come with an uncontrollable and ever-expanding circle of "friends". Path limits a users circle to just 150 people and users like that restriction so much that a million a week are signing up to the site. That's the sort of development that should be causing Facebook some worries - and rightly so.