[Update] Google Now, is now out of beta and working on the standard version of Chrome and has more cards like, Maps, Weather are available that the beta version of Google Now that was only available in Google Chrome Canary.
Google have now released Google Now on the desktop for Windows and Mac using the Canary Build of Chrome. To enable Google Now for your desktop you will need to be running the latest version of Chrome Canary which is currently v.34.0.1789.0. Once you have downloaded it, sign in to your Google account as normal, then type chrome://flags/#enable-google-now into the address bar and hit Enter.
Click the drop down arrow and change the setting from Default to Enabled.
Now at the bottom of the page hit Restart Now.
Now after Canary has restarted you will notice that the Alerts Bell is present in your Task Bar. Simply click it to view your Google Now cards.
Currently the Google Now cards that are available is minimal but hopefully that will change.
To see what you alerts currently are set for on the desktop version of Google Now, hit the Cog icon when the alerts window is open.
That’s it. Enjoy.
Note: Google Canary is designed for developers and early adopters, so things may break every now and then. You are able of course to use your regular stable version of Google Chrome as well if you wish. Google Now for desktop is currently only available in beta for people using Canary.