Old thread, old boat, new owner 
Just got my new to me '05 Chatham 18 and took it out on the water for a first time today. The fit is good for me at 6'4" and 200lb, 36" waist, size 15 US feet. The boat I have did not come with hip pads and I would estimate I only have probably 1/2" at the most on each side, probably less, between my hips and the vertical seat supports. Similarly, there isn't a whole lot of extra space to the side of my thighs, so this boat is great for tall people, but I would not necessarily think anyone with a waist size much more than 42" would be comfortable in it. But that's hard to tell as individual body types and preferences vary a lot.
The front deck does not feel tall at all for me, even for use with a low-angle stroke and a Greenland paddle.
The stability profile is very friendly: well-defined primary stability (boat is not twitchy just sitting in it) and a nice, supportive secondary (can sit the boat on edge and it will stay there). Granted, this is a 20" boat so there is only so much it can offer in final stability, but it won't take you by surprise and will give plenty of warning.
I did not find it exceptionally maneuverable, but probably more on the "maneuverable" side of things as long boats go (it is not stiff tracking). It responds nicely to edging for course corrections and turns, but I don't think the ends released for me unless I put it pretty much at a 90 degree to the water. So it won't "spin" for me without an unreasonably strong edging.
The bow pushes water to the sides and makes noses and splashing after a certain paddling speed is achieved, and creates lift even on flat water. The boat does not feel slow, but does not reward power with speed like more streamlined designs do. Feels efficient to paddle below certain speeds though.
The Valley hatches had all dry-rotted and lost integrity, despite being maintained with 303 and looking brand new inside and out (i.e., smooth and shiny but weak). They are unsafe to use on the water - as I was closing the rear one, a huge crack (6") opened in it and it could not be taped with duct tape due to the non-stick surface from the 303 applications (both inside and out). I will be replacing them with Sealect hatches (I think).
The deck rigging does not allow a spare Euro paddle to be stowed on the rear deck. My particular boat may have had its deck rigging changed and it is missing a large loop across the deck behind the seat (only has short diagonal loops, too narrow to fit a blade under them).
The seat and backband are comfortable for me. I like the ratcheting mechanism, but apparently the plastic on this ages - one of the release knobs broke on my first try at adjusting them. Will need to replace.
The footpegs could be mounted higher and closer - I have them only 2/3 of the way out on the rails (10 or 11 notches are empty towards me on the rails).
The thigh braces are nice, but somewhat prevent knees together paddling. On the other hand, even with knees under them, my legs are not too splayed out - a quite comfortable position for me.
Hope to take it in some lumpier conditions soon :)