In Wednesday's filing for its IPO, Facebook said that one of its biggest challenges is how to make money from users who access the site from phones and mobile devices.

On the desktop, there is plenty of room for Facebook to present advertising, but the smaller mobile screens present less opportunity.

So, on which platform are you most likely to use Facebook? On your phone, your tablet or on your desktop? Are you using Facebook less and turning to other sites like Pinterest more and more these days?