I love this plugin and the incredible amount of features and template/styling options. Great plugin. Thanks for making this!
However, with lots of features comes complexity. I spent many hours learning and setting it. The result was very satisfying.
Some comments and findings:
1. The only way to display comments grouped by post seems to be create an instance in the "widget" form, uncheck the box "use saved settings for this instance" and enter non-zero into "Group at most __ comments each post" box.
2. I love the option "Hide comments by specific ids" -- allows to hide the blog owner's comments (those "thank yous" in response to each visitor's comment), and only display visitors' comments. However, it seems that the number entered in the "Group at most __ comments each post" box is not the max. number of actual comments displayed under a post, but the number of comments per post before filtering out the owner's comments. So, if you want to display up to 3 (visitors') comments per post, you need to enter 6 into the box "Group at most __ comments each post".
3. The box "gravatar will be __ pxs wide" does not work with the plugin's CSS, because the latter is hard-coded to use 40px images. It was not a big problem because I found it easier not to use the CSS provided by plugin anyway.