With this reply, this thread should be officially closed (for the time being at least. When someone releases a very sophisticated system not listed here and it sits far above the rest, one can start this again). I have never used any Paid Solutions. So I cannot comment on them. But I have used and extensively tested the free kind. In my humble opinion, Drupal Commons is by far the best. Its the Undisputed King of Social Networking (self hosted) and the Poor Mans Social Script. Drupal Commons on Drupal 7 recently released
Social Niche provide a really friendly and hands-on service and community social networking software system - there site is: www.socialniche.co.uk
I'm using addmefast or youlikehits and really doing a great job for me to share my posts and increase fan following for my site. they are very simple site and can give you result according to your need.
What you actually need to do is [subscribe to content distribution] below in the signature section, so the "content distribution service" can effectively promote your newest blog posts to social networks and social bookmarking services without you doing the work. This gives you to grand opportunity to focus on creating quality content and not having to lift a finger to promote it on social platforms. Do you understand what I'm saying?