Not sure where within the site you;re looking at. I just went Dashboard -> Comments and used the search function at the upper right of that page to pull up individual comments and it worked fine for me. I searched for individual users by their username.
Not familiar with another method right off. At least not here.
Hope this helps,
-drmike
Last year I was able to click on a user and see all of their comments . This year I can't . I want to see the comments for just one user at a time for grading them for my class. I have 150 + students so something easy would be great.