I installed SezWho on this blog a few days ago and am really liking it.
One of the most significant PITA challenges in the blogosphere is managing comments. You can use services like CoComment, but my experience with their Firefox extension leaves a lot to be desired (it froze my browser frequently) so I’m not inclined to recommend it. Furthermore, CoComment does not rate/rank comments or plug into my blog to track other people’s comments.
SezWho does two things really well. First and foremost, their WordPress plugin drops a "was this comment helpful to you?" prompt on every comment. This binary yes/no is applied in two ways, first the aggregate ratings are presented in dashboard in my SezWho account, which gives me a unified view of what comments are posting and what people are ranking their usefulness as.
Secondly, as more people rate a comment up/down the ranking increases or decreases accordingly, which helps visitors pick the comments that are truly useful. On this blog I am not fortunate enough to have hundreds of comments on any given post, but on high traffic blogs I can see how this would help me as a visitor increase the signal-to-noise ratio.
I can imagine a number of scenarios where the aggregate user profile that a SezWho user generates would be useful as a cornerstone for a relevance engine. In other words, using knowledge about what you find useful to help you discover new things that you would likely find useful.
Lastly, I was really impressed that I received an email from someone at SezWho today saying "hey we noticed you installed the plugin, tell us what you think". A little outreach goes a long way with me.