As Google Blog notes, there's now a Google Video Player for Mac. Why would you want to use it instead of QuickTime? Now you can buy videos from Google Video Store, browse scenes within a video using thumbnails and play the video without waiting to download it completely.
This is the third Mac software produced by Google, after Google Notifier and Google Earth.
Google Video Store launch
Download videos from Google as AVI (for Windows users)
Play and convert any multimedia file (free software)