Lately the different browsers have been adding support for the new features of HTML5/CSS3/etc at a very rapid pace. Of course, features don't appear right away in the stable releases that everybody runs, but rather in various alphas, betas, and other pre-releases, with the most bleeding edge being the nightly builds. These builds are (usually) compiled every day, reflecting the current state of the source code repository, with all the latest changes made by the developers included.
I made a Mac OS X app for each browser (Apple Safari aka WebKit, Google Chrome aka Chromium, Mozilla Firefox aka Minefield, and Opera) that checks if a new version is available, automatically downloads and installs it, and then launches it. If you already have the latest version, it will launch or focus it directly, allowing you to have only those 4 icons in the dock, and always use them to access your browsers.
For those interested, these apps consist of bash scripts embedded in AppleScript app-bundles, so you can modify them for your own needs (note that by default they are setup to install Intel and/or 64bit builds when available). [crarko adds: If you look inside the application bundles you will find the scripts.] Please share any enhancements or fixes you might make.
Check my blog for the latest download link. If one of the downloaders fails it's likely that the URL changed, and I keep the applications updated as needed.
[crarko adds: I tested the apps, and they work as described.]

