Everyone sees your comments, but you don't necessarily know what everyone else's comments are about. Some things are interesting and pertinent to your world, but others are just random tidbits of someone's life (mmm... hot dogs...).
I've been asked "what's the point?" by people who don't live online, and honestly, I don't know that there is a point, any more than socializing with coworkers or business associates ever has a point. It's part of the human experience and it doesn't have to have a point.
It brings to light how much random energy is flowing. I was going to say "flowing through the Internet" but the Internet is just a communications medium for society as a whole. I think the Internet may amplify the energy, or at least give it a sense of focus. Note that I say "a sense of focus" -- really, there isn't much focus in our lives online, no matter what you want to think.
Not to sound to philosophical, but focus must come from within, and I'm in a generation, in a long line of generations, who are accustomed to being given focus from the outside. The idea that you need to find your own meaning in random bits of information is as old as the I Ching, but adapting the western mind to finding meaning is tough.
Of course, there's plenty that's meaningless -- well meaningless to you. Or maybe, meaningless to everyone. It's part of the human experience to simply exist and share with others, and that can be enough meaning.
The greatest part of the new model of social networking is that it's breaking down some of those barriers we built up in our post-modern world. We don't have to save it all up and remember we saw a man carrying a raccoon, we can shout it out, and everyone gets to know us a little better because of the weird shit we talk about all day.
I learned about the earthquake in Los Angeles via Twitter, and about the changes to the surface of Mars. I went to the community wireless event at the Lucky Lab last night because I saw it mentioned on Twitter.
I think the "point" is to enrich your experience as you go through life. It might be business, it might be social, it might just be vicarious living. No matter what, it's about doing more than getting up, going to work, and going home -- however you find that is up to you, but I think the tools are getting better to help us all do that.