I'm a fairly private person, but what fascinates me most about these new tools is the ability to not lose touch with people I know. When I was growing up and meeting many new friends or associates through school and camps, I always thought to myself that I would like to be able to keep in touch with everyone, but I didn't know how. I imagined keeping a very long Rolodex with everyone's contact info in it and going through it every year and just saying "hello" to each person I had met. I realized that this would quickly grow tiresome or difficult or impossible time-wise, but it was sad to give up. I remember meeting good, interesting people while traveling and always feeling sorry to have to say good-bye.
I haven't been the best at keeping in touch with everyone I know, but I hope that by understanding how to use the new tools out there effectively, I can do better. I'm wondering whether this same motivation is what fuels others to tweet or whether it's something else. Someone I recently met told me they tweet/fbook/geolocate everything for documentation purposes and to keep a permanent record of their life so they and others don't forget. At first this seemed odd, but after considering it for a while, I think this reason makes a lot of sense as well. Perhaps my sadness in leaving someone from my travels is similar to the sadness of forgetting something interesting about one's life.
I doubt I will ever really understand why others use these tools differently than I. Hopefully I can just one day understand how I want to use them for myself.