You may, or may not, remember the days of the "First Look" client - there were quite a few of them over the months with Voice, Windlight, etc. being testable on the main grid as a "First Look" when it was getting close to release (after the Beta Grid).

Well, with the ability that the last few updates have bought to run different clients on the grid, there is now an option to run the release candidate for 1.18.3 on the main grid, and this will continue with future releases. First Look will continue - as a main grid test for significant new features like Windlight, these release candidates are the final step of the testing process for bug fixes and minor new features. 1.18.3 contains fixes for about 60 bugs, some are tiny, some are huge (More > > will remain open on the edit window across sessions will be huge for every builder and scripter out there). The blog post makes it clear this process will be the norm from now on, letting you stay on the forefront of bug killing if you choose.

[UPDATE] If you do this, be prepared to reset EVERY part of your preferences you've changed!
[EDIT] Only about 60 bugs, 65 to be precise. I read the blog 3 times and read it as 635 each time... thanks Jayden