I have been trying out Google's new Chromium browser for OS X and it is quite impressive. Chromium is rather nimble and the rendering engine is rather bug free. I have run actually released web browsers that have mangled web pages beyond recognition and this one I have yet to run into issues. While there are a lot of features that are not working such as flash support and some of the configuration options are missing its is still quite a usable browser. I have found it is even more robust than Safari and Firefox on my mac for crashes.
I really can't wait to see what the finished product is like as right now the browser is quite usable and stable already. Do keep in mind however that if you decide to try Chromium its not "quite" finished yet and you won't be able to use it as a primary browser. See this entry in the Chromium blog for more information. Developer Documentation can be found here. And if you want to put Chromium through its paces check out the Chrome experiments site out.
One of the things that makes Chromium interesting is its multi threaded. Each browser tab is a separate process on your system. If you look at the output of ps or top you will see these processes running. Killing one of these processes will kill the tab and give you a cute sad mac icon in your browser. What is also quite interesting, the process is created only when the new tab starts to load content not during the creation of the tab itself.