Statistcally speaking, 67% of this product could be better

Eoin,
We don't have any modules that show the number of comments or most commented, etc. It's something we have in our to-do list as it is possible to fetch the number of comments from Facebook, store it in the db, and then create a module to display that info in new and exciting ways. It's not our top priority, but is something we started late last year, but got sidetracked by some other features and issues before getting it implemented.

Until then, if you weren't aware, if you're using the JFBCContent plugin to automatically add comment boxes to K2 content, you can show the number of comments per article in blog views. To do so, in the Social configuration area, simply set the number of comments to '0' for blog views. Then, in any blog views, at the bottom, instead of the gigantic comment box, will be a line with the number of comments. A user can then go to the article to see all comments.

Not as perfect as what you're looking for, but hopefully a start you can live with.

Hope that helps, and don't mess with my man-hood!

Alex