SQL Server 2008 RC0 comes with a Readme file and a Release Notes file. It’s always good to read both. In this RC, the readme file contains information on installation and upgrade, and the Release Notes file contains information about things that have changed from previous releases.
In RC0, they’ve changed the syntax/format of a few relevent new features. The changes affect T-SQL MERGE, the HierarchyID data type’s methods, and the Geometry data type’s Latitude/Longitude order. These won’t be doc’d in BOL under What’s New, because the What’s New section lists new features, not features that have changed since the last CTP. Reading up on features that have changed will (hopefully) reduce the number of “why doesn’t this code example that I downloaded from a reputable source work?” questions.
In addition to the two new performance features I just blogged about, RC0 also contains the new “Spatial Builder” API. Isaac has an excellent blog post about this API, with a (now-)working example. Check out his blog, I didn’t find this feature mentioned in either “What’s New” or “Release Notes”.