I previously wrote about a few lessons I've learned from my writing group about writing and interpreting comments. Here are two more.
3. An apparently useless comment may have a hidden message.
It often catches me off guard (and mildly annoys me) to see comments that seem totally "out there". Comments like "this appears to be the core of your paper" when referring to a tangential sentence, or "this sentence is probably not necessary" when referring to a crucial summary sentence. These and other questions/suggestions that demonstrate the person's lack of understanding are frustrating and discouraging. However, while the content of these comments might be useless at first glance, the comments become helpful if you read between the lines. These "useless" questions and suggestions indicate that some aspect of your writing (whether a specific sentence, paragraph, or the whole paper) led to a misinterpretation on the reader's part. Now the onus is on you the writer to identify the cause of the confusion and remedy it. This process is of course facilitated if you can have an on-going discussion with your commenter (see #4).
4. Commenting should be a discussion.
My writing group tends to use Google Drive for editing (although Dropbox is sometimes necessary for more polished and formatted pieces). Google Drives facilitates active discussions rather than one-time static revisions and comments that are common with printed paper or Word's track changes. The writer receives email notifications when people comment his/her work, and the commenter receives email notifications when other people (commenters and writer) reply to those comments. This conversation style of editing (while distracting for those who keep their inbox open all day) allows writers to ask for clarification if a comment is too vague. It also permits the easy agreement or disagreement among commenters, which can help the writer decide if a comment is one person's opinion or a general consensus.