Version 3 brings improved renderings of web pages, error and bug fixes, and a huge increase in speed. I immediately noticed a difference in the speed that many web pages were loading. There is also a difference in how the new tab page works and some nice improvements in the omnibox - this is where Chrome uses one box for both web addresses and search.
For a great review on Chrome 3, check out Lifehacker's article. Lifehacker is a great web site that covers a plethora of topics, from technology, to home improvement, to finances, and more.
If you already have Chrome, just click on the wrench symbol at the top right of the menu bar and click on "About Google Chrome." It will automatically find the update and you can install it.
If you have yet to try Google Chrome, simply go HERE to download and install it.