FWIW, that Join link seems to be non-functional in the new forums. (I tried on iPad and Mac Safari.) Meanwhile, as a workaround in case it helps anyone, I think I managed to submit my join request anyway—by the following steps: 1. View source on the main forum categories page, and search for "join here". 2. Copy the URL associated with that link, and paste it into the address bar manually to go there. Here it is, in fact: http://forums.toucharcade.com/profile.php?do=editusergroups 3. You'll see a Join Group button, but don't click it yet, First, find a little yellow dot on the right side of the page, a little above the level of Join Group. Click that dot, THEN click Join Group. Voila!
Is the Private Developer Forum still active? I tried joining it but never got a response, made me unsure as to whether is was still in use.
I don't think it's super active (hard to imagine it could be as active as the public forums) but it's still a place to ask questions aimed only at other developers, and/or share stuff semi-privately. I joined recently at it worked (I was approved by the next day). Maybe try again? I'm not sure how often they check the pending approvals.