Don't blame the platform for enabling people to be who they really are.
I think the issue here is that McLuhan was absolutely right when describing how the medium actually transforms and filters the messages that are sent through it. It's worth reading "Understanding Media" (or "The Medium is the Massage") because one of his key points is that the apparent content of the messages being sent across a medium is a distraction for what's really going on (the societal change brought about by the medium itself).
In the case of social networking the medium is broadcasting a message that it's normal to continuously stream updates, pictures etc. about your daily life as if the people following you cared about that. The fact that they do care about it is simply a sign that the medium is shaping society to the social network's particular medium.
Also, it's worth considering the difference between a one-to-one sharing of something (let's say a picture of your child shared with your mother) and the broadcasting of information to a chosen social group.
The former is a personal interaction which has many subtexts (proud parent showing off their child, wanting to connect with your own parent), whereas the broadcast does not have the same depth. It's just "look at me".
On the other hand, isn't this position essentially saying that because the things in your life are similar to others and not surprising, they aren't valuable and worthy of documentation?
What's wrong with "look at me?" Am I not worthy of being looked at by my friends because I haven't done something remarkable? Just because my kid isn't really all that different from every other kid, or thousands of other people were also at that concert (and my photos are mediocre at best). . .
And if I share something actually remarkable that I've done, it's just "bragging," right?
I don't log in to facebook very often. But when I do, what else should I expect to see but what's going on in their lives?
My instinct is the same as yours--to hold back and be private. To not share my life with others, because they might be bored. To not document my everyday triumphs and failures, because they're not really that different from anyone else's.
But I have a sneaking feeling we might be wrong about this one. Maybe our boring human lives are worth documenting and sharing.
However, I think jgrahamc and you are speaking to different things. There is documentation, much like our parents did when we went to the beach as a toddler and we took that picture with mom and the sandcastle, and then there is personal curation that lives in narcissism and strikes me as dishonest (or too honest, perhaps).
There is sharing triumphs and failures, and then there is bounding triumph and failure with one's personal accounts as to make the world about the documenter instead of about the documenter as part of, well, the world.
I'm not sure I have this idea completely worked out as this seems subjective and who can really judge another's motives with absolute certainty. All I know is there is a fine line and we would be careful to hold ourselves to a standard that encourages sharing life without making life about ourselves.
After all, you can't be open source (which we LOVE) when you're all closed-sourcey yourself.
Anyway, just a little food for thought that came into my head with your observations.
I take pictures of my kids, things we're doing, or interesting things that I see in my daily life. When OP says "narcissism", he's either following much different people than I do, or he doesn't know what narcissism means.
We're just so immersed with our own life, that we never stop and consider whether others would actually care if we shared something.
And a platform can enhance the narcissism. Take any humble person and throw him into Twitter, and he/she can't help but tell everyone about their great life, or how they suffer more than others.
Publishing all your pictures, all the time is like carrying a projector with slides from random moments in your life to every party you ever go to and setting it up for everyone to see whether they asked you to or not.
It sounds like a crazy thing to all of us who are aware of how things used to be.. but maybe for the next generation this is going to be cultural norm. I don't want to be judgmental and I'm not a psychiatrist so I can't tell if that's positive or negative or even if it's a long-term or short-term phenomenon, but at least for right now, that seems to be how we're evolving.