Microsoft has released a word document which explains all the AD schema changes for Exchange 2010 SP2 to install and work properly. Download the doc here. To my surprise, the same doc has all the AD schema changes for Exchange 2007 & 2003.
Though the doc is only 1mb in size, it is packaged in an msi file, which needs to be installed.
Once the installation of the package is complete, the doc is available.