I'm going to start off (which is funny that I say that, because I really don't ever type enough to justify an opening like that) by saying that I really haven't read the majority of these posts, not out of ignorance but moreso because I really just don't have the time or willpower to examine the way everybody feels about words, nor do I expect anyone to do the same to me.
However, my biggest problem with forums is just as my opening statement - I WANT to be able to have a lot to say, I want to say it intelligently yet legibly, but I can't do it. The only advice I'm given is to read more books, which while I don't do that, I can say that I read more each day on the forums than an average 15 year old (Oh, hey, my age!) reads in two weeks (if that's really saying much). I've signed up to three website's word-of-the-day programs, but I don't feel I'm improving my use of words because of it, and regardless my length isn't getting any better.
As for your underlying point, do I alter the way I normally speak in real life to communicate with others on The Escapist? Yes, and at great lengths. I am a huge redneck in real life. Outside of discussions in the classroom (which happen way fewer than I would enjoy) I talk with such little care for the English language because it's the first thing that comes to mind and I don't much think before I speak. "I couldn't really say I agree more," becomes, "Dude, the hell you talkin' about?" in real life, and it's really, honestly not because I'm an ass, it's just the way my mind thinks. Which is a reason I love forums; nobody is waiting on their toes for me to respond to them, and so I can take my time and compose a sentence the way I want it to read.
To bring my short discussion home, it's a huge joykill that I can't express myself the way I want to. I can say that sometimes when I'm writing a response, be it on any forums, I've been known on occasion to take five or ten minutes to figure out the way I want to write a single sentence. It really is important to me, and I can't seem to do it.
In conclusion, yes, I type differently than I speak, I feel it's useful as long as not overdone, and I wish I knew of ways to improve both the way I speak and the way I type.
EDIT: Ouch, now I'm out of order, but I thought of something I had to bring up. The biggest reason why I've been visiting forums in the past two years and taking part in many conversations as I come and go and the reason why I have such a desire to speak more figuratively with interesting thoughts is because for quite a while now I've wanted to be a song writer. I listen to a LOT of music which stems from the fact that I've always spent a lot of time on the computer and because of my love for music there's often times where I hear a new song with a cool lyric and I just think "Wow, how did I not think of that?"