If you have to send mail or message to people you want to interact with, it's more personal and works better.
I know this is anecdotal, but HN is the cause of a lot more of the bad things from social media in my life than Facebook is. Because I only use Facebook to organise events, meaning I log on two or three times a month. On the flip side I’ve just wasted five minutes of my life replying to you. I mean no offence by that, but there is fair chance we won’t even talk here because you may not see my reply (and I might not see yours if you do), and we’ll certainly never speak to each other again.
I think this blog-entry is insightful and well written, but are we going to remember it in two hours, or is it just another “baby picture” on the HN news feed?