We have to remember that "For now it's only a very lightweight signal — affecting fewer than 1% of global queries, and carrying less weight than other signals such as high-quality content" (http://googlewebmastercentral.blogspot.co.uk/) and i would advise not rushing in implementing a full site wide HTTPs.
HTTPS generally slows down site speed and as we know, site speed is a key ranking factor, so this has to be treated carefully, along with all of the other points mentioned above.
I would wait, lets read some case studies and as many of us know, there are so many other stronger ranking factors we should be concentrating on during this first announcement by Google.
