The encryption protects only data that travels between an your browser and the Google search server. When people click on a search result, they go through the encrypted channel and are directed to another Web site. The encrypted connections to Google.com means that users in China and other regimes where Govt surveillance is in place will be able to conduct searches without governments knowing the detail about the search. The secure Web search option is going to slow down the initial connection between the computer and the Google server. Additionally, it also means that Google will have to use more processor power to handle SSL connection, which is the biggest reason most Web sites don't offer it as an option.
source : http://blog.taragana.com/index.php/archive/google-launched-encrypted-web-search/