We're adding in editing of comments but I'm not sure about a preview capability because comments are meant to be small and succinct with no line breaks (hence little formatting and ideally no line breaks).
We're also adding a series of moderation facilities so moderators can control the flow of a question, e.g. convert a hijacked thread answer to a new question, convert answer to comment, etc. This will help future visitors get a better handle on the information presented.
You may also have noticed that there is a "subscribe to future answers on this question" next to the answer reply. Originally as a respondent, you only received updates on comments for your answer but this has been changed for those wanting all replies to have an option to do so.
We do also know there are some formatting issues, especially when using any markup that is not enclosed in a code section (please use this where possible!). Added to this, we want to auto-link urls that have not already been linked.
A complete guide for formatting can be found in the upper right hand corner of the text editor under "how to format" or via the direct link here.