Google has been migrating all their properties to work over SSL over the past few years. Google would like to see you make your site work over SSL as well. So much so that Matt Cutts said at SMX West that he would personally love to make it part of the ranking algorithm.
Data from Google Chrome usage shows that more than 70% of Chrome users are visiting HTTPS-enabled websites, which indicates that browsing via HTTPS is becoming the norm. Armed with that data, Google is taking steps to “encourage” the global adoption of SSL/HTTPS.