I think there's little need to repeat the major advantages and disadvantages Google Chrome offers compared to other Mac browser mainstays like Safari, Camino, and Firefox. Chrome obviously brings with it lots of speed and a more polished interface (tabs on top done properly), but the real deal here is less obvious to casual users: process-per-tab, which makes sure that a misbehaving page cannot bring down your entire browser.
On the disadvantages end, the extension framework for Chrome is still not ready, and is also not part of the Mac beta release. Firefox' extension ecosystem is one of the major reasons users stick to Firefox. A few features are also missing, such as the bookmark manager and support for Google Gears.
In return, Mac users get features that integrate the Chrome browser quite well with Mac OS X, something Firefox is still working on, even after all these years. Chrome for Mac taps into Mac OS X's native spell checking and keychain architectures, and also sports various Mac-specific animations. The interface is also as Mac OS X as possible, which helps in making the browser feel like a native citizen on your Mac. On the technical side, Chrome for Mac uses Mac OS X's native sandboxing features.
The beta release is available for Leopard users and up, and only works on Intel Macs. You can download it from the download page.