Forums thrive on conversation.
If there's a thank you button, I think there should be a no thank you one too. Biased otherwise.
cheers,
Toddy
Why not have a range of buttons:- 'no' 'thank' 'you' 'what' 'he' 'said' 'plus' 'one' etc to reply you could just select the appropriate buttons therefore negating the need to type a reply. Hey there could be quite a few buttons.