I pretty much agree with what's been said. ^
In my experience, half the people who use "big words" don't know how to properly use them. (Personally, I prefer the proper use of grammar over a broad vocabulary.) The other half are people who try much too hard to seem intelligent and forget that one of the most important aspects of communication is having your message understood, not making it harder to comprehend.
I definitely agree and tailor my dialogue to meet the level of intelligence of the person(s) I am talking to. I will pepper that dialogue with more complex terms and often supply working definitions to broaden scope, but keep an eye on the listener to see if they are following. One of my greatest attributes is the ability to break down complex ideas into very small bite size pieces that even children can understand. In all cases, I keep looking at the person to see if their eyes have grown dull or glazing over or if there is that sparkle of recognition. It saves a lot of time.
The other day, I was in a conversation with a fellow who is mentally handicapped due to a terrible accident when he was a small child. (He was run over by a car while riding his tricycle - the family doctor, who was backing out of their drive way, no less.) He asked me what I thought of our newly proposed taxation system, the HST, and I explained it briefly to him and the problems associated with going back to the old system. To my utter surprise he said, "Is it like this.... blah blah blah blah" and at first, I didn't get what he meant and was preparing to clarify what I meant. Then it dawned on me that his very, very simple analogy was, in fact, very appropriate and I agreed with him the way he was looking at it.
All in all, it was a bit startling to see how he boiled down my simple explanation, into an even simpler explanation that fit to a T. It was interesting seeing it happen "live", that moment of cognition and recognition... and having his idea validated. I'm pretty sure that doesn't happen much for this fellow.