My .02: I raced the 250 class (back in the 2 stroke days). I started in 1996. 2004 comes around and I want a 4 stroke, so I assumed I would get a 450 to stay in the same class. I test rode a crf. I rode up the shute to the starting gate at area 51, clicked 3rd and whacked the throttle and nearly fell of the back. It's a lot of bike. It can get out of hand really fast, and throw you into the ground much harder than the 250 2 stroke. I have seen it many times where kids that feel like they need a big bike, and I've heard them brag about their big bike. I've also seen them eat shit because they can't handle it.
I love my 250f and would be more than happy to let someone ride it before they make a decision on a bike. Maybe Matt will let your buddy test ride his bike as well.
The geometry and physics of a bike are different then a quad. If you land goofy, you can twist the throttle and dart it into a tree or off the face of a jump, and it happens instantly on a 450.