The younger folks don't even understand why (or how) they would want to upload images to the site. They just put them on Facebook or Photobucket (using the app on their phone) and post a link.
It's the way things are going, like it or not.
This sounds accurate for SOME - maybe even most - forums, especially those geared to style, gaming, celebrity and quickly moving subjects....
BUT, it is probably not accurate for more education topics. Examples - boat forums, R/C or "deeper" hobby forums, construction and how-to forums, etc. etc.
There are really two types of users - those who create content and those who consume it. Yeah, that's very general, but phone and FB users are much more likely to be the later.
The entire idea of a lot of forums is the sharing of information...which often entails more than you can type with one finger.
Not to say we have not entered the mobile revolution...we have. But each forum admin or owner should look closely at their target markets. If a forum is about parenting infants, for instance, it is very likely mom or dad may be at home in front of a computer or an ipad with keyboard, etc.
Just for comparison, my new (quadcopter, drone) forum has about 10% true mobile (phones, not pad!) visitors and my big old forum (hearth.com) has about 8%.
I think we could call this the tablet revolution....as opposed to phone....if my numbers mean anything! There are about as many or more ipad users as phones.....