Mark Bridge writes:

With Facebook’s stock market flotation expected to go ahead next week and a company value of between $77 billion and $96 billion being anticipated, the social network is putting the finishing touches to its paperwork.

It’s just filed an amendment to its original registration statement in which it warns that the increasing use of its mobile services may cause a problem. It’s not the technical infrastructure but the fact that Facebook’s mobile offering isn’t as well-established as its conventional web-based service. Facebook has previously admitted that it’s not making much money from mobile, which means there’s an obvious problem if people abandon the money-making web service for the mobile service.

Mobile ads have now been introduced - but at the moment they’re largely unproven on Facebook. And that could worry some investors.

“We had 488 million Monthly Active Users who used Facebook mobile products in March 2012. While most of our mobile users also access Facebook through personal computers, we anticipate that the rate of growth in mobile usage will exceed the growth in usage through personal computers for the foreseeable future, in part due to our focus on developing mobile products to encourage mobile usage of Facebook. We have historically not shown ads to users accessing Facebook through mobile apps or our mobile website. In March 2012, we began to include sponsored stories in users’ mobile News Feeds. However, we do not currently directly generate any meaningful revenue from the use of Facebook mobile products, and our ability to do so successfully is unproven. We believe this increased usage of Facebook on mobile devices has contributed to the recent trend of our daily active users increasing more rapidly than the increase in the number of ads delivered. If users increasingly access Facebook mobile products as a substitute for access through personal computers, and if we are unable to successfully implement monetization strategies for our mobile users, or if we incur excessive expenses in this effort, our financial performance and ability to grow revenue would be negatively affected.”