"Google Search will be redirected to secure google search connection(https://), if you are signed in" Google said in their official blog.  This will provide security for users search queries by SSL encryption.  They set SSL as a default connection for Gmail in January 2010, four months later they introduced secure search in this link:
https://encrypted.google.com/ 

Recently, Other Giants like Twitter, facebook also introduced the SSL support. 

As searching query is important and risky thing(especially if you are in public cafe), the google is introducing the default SSL encryption in google Search for Signed in users.  If you are signed in, the google search will be redirected to (https://www.google.com), usually it search in direct connection(http://www.google.com).

If you are not google user or not signed in, you can still use the Encrypted Search by visiting https://www.google.com directly.(Don't forget the 's')

Source:
http://googleblog.blogspot.com/2011/10/making-search-more-secure.html