This is interesting to see how Google identify relevant. It is based on a combination of the following:
- Direct connections from your Google chat buddies and contacts
- Direct connections from links that appear on your Google profile
- Secondary connections that are publicly associated with your direct connection
This is my snapshot social circle for example.
In addition to web pages from your social circle, posts from your Google Reader subscriptions may also appear in your social search results.
That you can see from above example of my Google Account, I have small number of contacts on my Gmail account and very less number of links on my profile, but I have strong secondary connection, mostly from Twitter. In this case, In my opinion, Google will give more weight to Direct Connections rather than Secondary connection. You can find more details on Social connections here : http://www.google.com/support/websearch/bin/answer.py?answer=1067707
It would be interested to experiment on this in different account and geographic. Will share to you guys soon.