Windows/Mac: If you've been using the Chrome beta or dev channel, you've been able to enjoy the benefits of Google Now cards right in your browser. Now, users on the stable channel get to join the fun.
The new Google Now cards utilise Chrome's built-in rich notification system to display cards it thinks may be relevant to you at the moment. You can click on the bell icon in your system tray to see a list of all your cards. The Chrome update is rolling out "over the next few weeks", so if you don't see it right away, make like a hitchhiker and don't panic.