How does your contribution evaluate?
Your sharing activity is useful, but retains an extremely limited value. Along the years, this investment may have no follow-up, and no benefits for your professional or personal activity. More likely, this investment might become a cause of pain if disinvesting is connected to a total loss. Think for instance that facebook, google plus and others might ultimately disappear!
Sharing and contributing
It can easily be understood that one can only share data that has been produced. So you should find a balance between what you share and what you produce. If ever you believe that the effort of synthesis and commenting that you attach to your shares is significant (hard on twitter, but easier on facebook, linkedin, posterous, googleplus) then you should definitely go for a different means of publication.
Create your own site or blog!
The only way to value one's contribution to the ongoing plantery effort is to create your own site, on your own domain. You may even understand the need to reaclaim control over the entire set of your data (files, pictures, etc...)
Buy your domain
This is easy, cheap, and will create a long lasting identity. Most blog or social operators allow for using one's own domain name on their site (posterous, google plus, wordpress...). This however is not the solution because you do not have control over your data and over htaccess redirections. This last issue is crucial: should you decide in the future to change your domain name, or to redirect the search engine ranking that you've created to another, say professional, site, you can't!. So:
Pay for your hosting
Most often, buying a domain name comes with a free or very cheap hosting, that is sufficient for starting an activity. Technically, a blog or small site requires a database, often present in low prices hosting offers.
Share your productions
What you plae on your own site, share! You may partially automate this process using tools like posterous.
US english is not your native language? Translate!
Providing your own translatations to your native language is a must. It is also highly rewarded by search engines.