Chrome now checks downloaded files for malware, and Google claims it has designed the feature in such a way that it doesn't have to know which URLs you visited or which files you downloaded to be able to detect malicious files.
You can now also fine tune the data that websites store on your computer, including Flash Player’s Local Shared Objects (also known as Flash cookies), directly from Chrome.
On the graphics front, Chrome 12 includes support for hardware-accelerated 3D CSS, which enables some nifty effects such as rotating and scaling videos. Try this Chrome Experiment to see some of the new features in action.
Finally, Chrome 12 brings several minor improvements such as an improved interface for setting a homepage and searching for Chrome Apps directly from the address bar.