It has been on Adobe Labs for quite a while and now it has been released as a final product that can be downloaded from Adobe website.
You can download Adobe Camera Raw 6.1 by going to Adobe website. Here are the links for Windows and Mac users:
You can also get an update straight from Photoshop CS5 by going to menu Help -> Updates.
If you want to check if you are running the latest version of Camera Raw, go to the menu Help -> About Plug-in -> Camera Raw.