Released today, Google Chrome 18 beta for Windows, Mac, and Chrome Frame improves 2D Canvas support and introduces a software rasterizer. The new features are not yet available on Chrome 18 beta for Linux.
Basically, this means that games and animations based in the HTML5 Canvas tag ought to run faster and appear smoother. Google noted in its blog post announcing the changes that this was hard for them to implement because of the "numerous hardware and operating system configurations" that people use.
It's complicated enough that to display 3D content on older computers or those running Windows XP, Google went out and licensed a software rasterizer called SwiftShader from TransGaming. SwiftShader only kicks on when Chrome's built-in GPU acceleration doesn't activate.
Adventurous types can see precisely what's being accelerated by typing chrome://gpu into the location bar, or can force SwiftShader on by adding the--blacklist-accelerated-compositing and--blacklist-webgl flags to the browser's command line.