Well.... ok.
The only questions I saw were about whether or not you should shutter your forum and pump up your Facebook and what my opinion was.
My reply was my opinion which I thought would lead you to an answer for the first question as well.
Sorry. I'll try and be clearer.
In truth no one can tell you what the future will hold. Blogging used to be "the thing" and now Tweeting is "the thing." You pointed out that kids seem to like brevity on the web. I would argue that if you have the attention span of a gnat you are only going to give a quick bzzzz before moving on.
In my experience those that are true fans of a comic are passionate about it and want to discuss all the minutia at length and ad nauseam. Having a place where they can do that and where you can interact with them seems like a very important thing to have.
Maybe you can have that sort of exchange through Facebook. There isn't much to Randy
Milholland's Livejournal account, he basically just posts updates and lets the dozens of folks who show up discuss among themselves. Jeph Jacques has a LJ too but he also has a forum that he has warned me off of as a bad place full of snobby Indie music lovers (NOT a fan of his musical tastes).
The Penny Arcade forum is a massive monolith of activity. Same goes for the Blind Ferret forums (Looking for Group and Least I Could Do). Gunnerkrigg Court's forum has almost 35,000 posts on it but only 2 categories.
My point is, that having a place where devoted fans can gather and share with each other and the creator is important. Most of the higher popularity comics do it with a forum of some kind or another. Some get by on a complex comment system and some use stuff like Livejournal. Can you make it happen at a social networking site like Facebook? Perhaps. If others can do it with Livejournal I don't see why not. The point is to have a place. Where it is and how it is put together seems less important.
In my experience if people aren't posting in your forum they probably aren't going to post on your comics facebook page either. But at the same time, if they are logged into facebook already, perhaps they may be more inclined to simply because it's easier.
But in six months Facebook could be the has been that MySpace is now. Something newer and hotter could come along and then what do you do? Randy and Jeph still use their livejournals even though blogging isn't really all that hot anymore. Will you still want to make Facebook your home if it goes the way of MySpace?
The ideal situation, to my mind is to do all the social networking stuff and funnel it into your forum because you will always have that because it's yours. But ultimately have that place is the important thing. Moving it around every so often as popularity of other sites trend may not be a great idea but that's another discussion. Hope that clarifies.