Often it happens that while you are answering a node, someone else is also in the same process and has answered before you hit the submit button. If possible, it would be a good idea to have it mentioned some way before you hit submit. So when you preview, if an answer has been submitted in 'last x number of minutes' or 'since you click the reply button', it will show up as a link. You can read that and may modify your answer in the light of what is already posted.
It could be a good idea from the content perspective. It may not be such a good idea from sheer enthusiasm perspective which keeps site alive by encouraging the active participation.