For those that use Safari as their browser and want to check out the nightly builds of WebKit (the browser engine in Safari) that are wrapped in the latest Safari application. Work on WebKit (including bugfixes and website compatibility mods) is happening all the time, but it only gets pushed into official Safari releases very infrequently.
This blog entry explains about nightly builds, while the actual depot for the nightly disk images is here.
If you want to make the WebKit nightly your default browser, just to into its preferences, select the General tab, and select WebKit from the drop down menu.
