I can't speak for other divisions as i only own TF2.
But basically in tf2 we use the private forums for only administrating information, and "keep in mind" type things that are important for administrating,
We use the general TF2 division sub-forum for talking about things relating to tf2 ONLY, that is to say stuff about the game, maps, classes, and even funny stuff that has to do with tf2.
when we need to talk about non-tf2 things we come to the general/off topic sections.
I think this is easier for us TF2ers since that division is much newer and was created near the time that eGO was becoming a one-big-unified family where ALL members belonged to ALL divisions (regardless if they own the game)
I'm not saying we don't occasionally get misdirected (troll) posts in our tf2 general sub-forum. But its rare.
I invite anyone who owns tf2 (even if you aren't active, or don't play it), or is just curious about the game, to come step into the tf2 forums and have a poke around.
I know that (especially with the CSS division) this was harder, because ya'll had houses, and people liked to only discuss stuff with the people they played with everyday. But i believe this open line of communication is not only better, but more inviting.
So please remember. if its about YOUR game specifically, post it in your divisions sub-forum. otherwise bring it here so we can all enjoy!