I do agree, with one exception. I do think it is important to post a picture, but I do not think that it needs to be a picture of yourself. There are a handful of people that I follow on Twitter that use other images and they happen to be images that “fit” with that persons persona. I do use pictures of myself, but I believe you can go the other route and still have a credible presence. In a society that places far too much emphasis on appearance, I think that there is actually something to be said for not using your picture.
Having said that, I think your fifth suggestion is maybe the most important. If you are going to get any real value of social networking, you have to be all about the social aspect of it. LinkedIn is a really good example. I have been on LI longer than I have been on any other community and there have been times when I have not felt like it was a very valuable place to be. That was primarily because I was not proactive in engaging others there. I do that a lot more now, and LI has made it a lot easier to be interactive with updates, groups, questions, applications, etc.
One of the biggest differences between the 1.0 world and the 2.0 world is the transition from monological communication to dialogical communication. There is a lot of value to be found on LinkedIn, the Ning networks, Facebook, Twitter and other places but you have got to take a dialogical approach…you have to be reaching out to engage people and you have got to listening to them. The people (and companies) that do a good job of this are getting a return on their investment.