AJAX comment preview (with preview button)

prototype's Form.serialize doesn't handle submit buttons very well, in
that submit buttons, no matter how many get serialized, no matter if
they are named the same or not. so for example, you would get

name=Bob
action=save
action=preview

so what i would suggest, is you detach the buttons from the form,
perhaps making them button elements and create 2 javascript functions,
one to submit the comment for preview and one to submit the comment
for saving, and then attach to each button via onclick.

each function would then submit to a different controller/action to
handle accordingly.