This is a great work. As some have stated before, a consolidated view of the comments all at once would be more beneficial when it comes to a user-friendly experience.
One problem I found from my own experience is that with the HeatMap AdAptive Theme (and I saw other users having this problem with other themes, too) the counting of the comments does not work correctly since it only counts the WordPress comments.
Other than that, this plugin is one of the best ones I have seen. It is well designed, well coded and very clean. Next to this, the little problems and the fact that comments are separated into tabs seem to be "unimportant", so I give this a deserved 4.
Note: I can't understand, though, why people are so negative about the tabs thing since if not for this plugin, most people would be putting only one service on their blogs. It could be better thought to eliminate the tabs (or give the option to, which would be the perfect solution), but come on, this is great work, I hope the author keeps it up to this high level!