With every major WordPress release, the support team creates a Master List to help users troubleshoot, and inform of common issues.
With every release, the common issues that pop up are generally different. Currently we just create a new post, and let the old one disappear into nothingness on the forums, where a new one steps up to take its place.
Although the old lists are still available, they're hard to find, and generally unorganized. By providing a version controlled history of the content of these, we make it easier to look notice trends, and also to find back to issues with specific releases (especially useful for sites updating from older versions).
The structure is split into directories and sub-directories. Although WordPress calls both version 3.0 and 3.1 a major version, for the sake of keeping the list easy to browser, we've opted to organize things into primary and secondary numbers.