The feature was previously available only for signed-in users
Google is now finally encrypting all searches originating from Chrome. Previously, only signed-in users had their queries encrypted in the Omnibox, all other searches were sent as plain text, meaning anyone wanting to intercept those searches could have done so.Starting with Chrome 25, currently in the dev and beta channel, all searches starting in the browser will be encrypted. Chrome is actually the last to enable encrypted searches for all users.
Google introduced encrypted search a couple of years back and has been expanding its use ever since, making it the default for signed-in users on the site in October 2011.
It's also available to non-signed-in users, though they have to explicitly use the URL of the encrypted version, but most people don't start a search from the Google homepage, they do it from their browser.
While users can choose to visit the encrypted version of the site, simply by typing "https" in front of the URL, they don't have that liberty in browsers.
In fact, at first, Google didn't provide HTTPS access via the search APIs browsers used. Once Google was confident enough, it started allowing browsers to make encrypted connections over the API.
Mozilla was the first to make the switch to encrypted searches. Starting with Firefox 14 in July last year, all queries starting from the search box or the AwesomeBox were encrypted for all users. Safari made the switch in September last year.
Now, Chrome is finally doing the same, encrypting all searches. It's not the first time Chrome is the last to make the switch to a feature Google itself is offering.
The feature is enabled for all users and changes shouldn't be noticeable. With the switch to encrypted search, Chrome also uses SPDY to connect to the search API, which should provide a speed boost, though again, the changes shouldn't be noticeable.