Google is missing the thing that Facebook does well here,
"identifying real people". [0] When I looked at the
"Friends" google identified it was really just connections I'd made with Twitter, flickr and various other services. Very few I'd met or consider a friend. Parsing data to find friends isn't as good as being sucked into the human
"social graph".
Identifying real people is a core concept at Facebook. and something they have got right (identity) and google will find difficult to replicate.
[0] I wouldn't have realised this point as quickly had I not read "The Facebook Effect" ~ http://www.amazon.com/Facebook-Effect-Inside-Company-Connect... which despite its flaws gives some useful insights. Excerpt: http://techcrunch.com/2010/05/06/facebook-david-kirkpatrick/