Use LinkedIn to build your reputation with Google
Here I need to admit that I have no firm evidence, but I have a strong feeling that Google pick up you profile in LinkedIn, indexes and give you more credit in form of page rank compared with your profile in other social media.
This is the main reason I build a LinkedIn profile. Another reason is that many of the people I network with, have their profile on LinkedIn.
There are more career oriented corporate business people on LinkedIn, so I strongly believe that you must benefit from building a profile there as well. Again I think that Twitter is the right way in because you will need more connections than you family and friends and I don't believe in approaching strangers and ask them to join your network.
You may notice again how valuable Twitter is, with its casual social rules where its fine to just follow and follow back. Without Twitter it's really difficult to build huge numbers of friends and connections on the other social media without being accused of spamming.
Please comment on this information below so I know what you think. Maybe it can result in a great discussion. I think that everybody should contribute to the development of this content.