Great questions, Maureen, but you might be right in that there is a lot in here! So let me handle a couple of the questions and see if someone else can help with the others:
3) Here are some demographic analysis of
Facebook
and
Twitter
. I do find it interesting that Twitter supposedly has a less affluent user base but a high percentage of college graduates. Makes me wonder if the data is a bit messed up there. I'm sure MySpace numbers are out there, too, but from the last thing I saw, they are generally younger and less affluent.
4) In the above stats, notice the number of young site users, and on Twitter, see the numbers without children. That might help you a bit.
Also, I don't know if they are up yet, but there was a presentation at AIM last week that broke down a specific company's use of different ILS's. I'm sure results will vary company by company, but I would check out those presentations once they put them up.
Good luck!