Rich desktop notifications have been available in Google’s Chrome browser for the Mac for some time now, provided you were on the Canary channel where Google hosts early and unstable alpha releases of its browser. The normals, however, had to wait until desktop notifications for the Now cards made their way into the stable Chrome channel.
According to Google itself, that day is today - people on stable Chrome releases should start seeing Google Now alerts being pushed to their Macs and PCs. The handy alerts are nested right inside the browser’s notification center that sits in your Mac’s status bar (bottom-right if you're using Windows)...