This blog is updated daily..
A general description is here.
Help in base and recommended packages is no longer zipped: text, HTML, latex and examples files are now built when needed.
Options --use-zip and --use-zip-help in R CMD INSTALL are no longer available and --auto-zip only zips data (or not).
Help in packages installed under 2.9.x may not work correctly, and a warning is given when such a package is attached by library(). Re-installation of all packages is advised (use update.packages(checkBuilt = TRUE)).
Binary packages are installed without CHM help if they contain it (as those intended for 2.9.x may).
The help default has been changed to be HTML help rather than CHM help. [Not yet the MSI installer.]
Binary packages are installed without CHM help if they contain itfor the standard installer is HTML help rather than CHM help.
The categories in the installers have been simplified. Now the files to support installation of source packages are always installed (they weare now only 0.7Mb), and there are no longer categories 'chtml', 'html/help', 'latex' and 'Rd'.