As several commenters pointed out on this post, there's not much difference between virtual and "real" face-to-face communication except for the medium you use. The same rules apply: remember your manners, put the other person at ease, be cheerful, be gracious.
That is the premise of my post over at Search Engine People. In my several years of exploring the blogging medium, I've realized how powerful commenting can be as a way of making new contacts. If you leave witty insightful comments on someone's blog, they or their readers may want to follow you back to your blog and see what you write.
You can find people whose views you agree with, and a blog comment saying so might even lead to a friendship. (I have several friends whom I've got to know through blogging, and I know that's pretty common.) You can also get business opportunities. The reason why I was invited to post on the Search Engine People blog in the first place is because the editor liked a comment I left on a post there.
And if that's not enough to get you to go over and read my post, here is one of the tips I share:
Use coasters. If you go to a friend's house and place your glass of wine on their new coffee table (carefully ignoring the coasters he has placed there) . . . however much he's enjoyed your scintillating conversation he's not likely to think about you very favorably the next afternoon as he is trying to scrub the ring off his hardwood table. What's the online equivalent of not using coasters? Making more work for the host: writing incoherently or with poor grammar, leaving broken links, making a claim with no references etc.
So how do you win friends and influence people just by commenting on blog posts? Read the rest of my post and find out!