Well, this of course points out that there are not many online equivalents of going to a friend's party, volunteering with others or a business mixer -- facilitated real-life scenarios where people are, effectively, socially introduced. Somewhere you can meet someone, have some one-on-one chat and maybe exchange a business card, phone number or email address. That's a socially acceptable starting point for a friendly relationship.
People need those starting points. If you meet some guy at a TechCrunch party and talk for a couple minutes, it is perfectly acceptable to email him with some question a week later. But if you just comment on a blog post he makes, even if he responds in another comment, you're still effectively a stranger. You can email them, but it better sound a little apologetic. You sure as heck aren't going to ask to add him to your social network.
There's still nothing stopping you from emailing him a question after that kind of exchange on a blog, unless he doesn't post his email address publicly.
I totally agree (I'm reasonably comfortable with total strangers emailing me), but if I, say, meet someone at a trade show then there seems like there's a higher level of acceptability to it than "hey, remember me, I responded to your blog post." Maybe it's just me, though?
And I have to disagree with this... or at least, I don't want the distinction to become arbitrary. The Internet and Web were meant to make communications easier. But it seems like all this online social network crap is replacing real world meet-ups.
People need those starting points. If you meet some guy at a TechCrunch party and talk for a couple minutes, it is perfectly acceptable to email him with some question a week later. But if you just comment on a blog post he makes, even if he responds in another comment, you're still effectively a stranger. You can email them, but it better sound a little apologetic. You sure as heck aren't going to ask to add him to your social network.