This blog is updated daily..
A general description is here.
A field containing just a sign is no longer regarded as numeric (it was on all platforms in 2.7.0, but not on most in earlier versions of R).
CITATION files are now read in Latin-1: quite a few were failing if used in a multibyte locale such as UTF-8.
Quartz draws contiguous lines much faster
is() was wrong for some S3 class objects with multi-string class.
undoc() / codoc() where not checking all S4 methods in some cases.
Because of a typo, 'pointsize' in png(type="cairo")
etc devices was being interpreted in pixels not bigpoints.