This blog is updated daily.
A general description is here.
The folder selection dialog used by choose.dir() and File | Change dir is now re-sizeable with a status line showing the currently selected path. The workaround for Vista mentioned under '2.6.1 Patched' is now applied only on Vista and later, rather than having a separate 'Browse' button.
Rgui has been re-written to work internally in Unicode. This means that copy and paste will be done in Unicode, and should now work correctly if R is being run in a different locale from other applications. [Not all parts of CJK support have yet been tested.]There is more support for input methods, thanks to Ei-ji Nakama.
The new argument dyn.load(DLLpath=) was implemented to make DLL conflicts easier to manage on Windows (see ?dyn.load), and is used by package tcltk. This changes the meaning of the environment value MY_TCLTK: its value is now the path to the directory containing tcl85.dll and tk85.dll.
The GraphApp DLL is now called Rgraphapp.dll to avoid any confusion. Packages using it (Cairo, RWinEdt) will need to be re-installed for R 2.7.0.
The listbox used by select.list() now responds to double-clicking an item (as if the item had been selected and then the OK button pressed).
Browsing for a directory in choose.dir() and the Rgui 'Change Dir...' menu item now works around Vista's confusion about 'desktop' by starting at 'My Computer' on Vista/Server 2008.
The definition of 'whitespace' used by the parser is slightly wider: it includes Unicode space characters on Windows and in UTF-8 locales on machines which use Unicode wide characters.
dyn.load() gains a 'DLLpath' to specify the path for dependent DLLs: currrently only used on Windows.
[dpqr]gamma(*, shape=0) now work as limits of 'shape -> 0', corresponding to the point distribution with all mass at 0.
o The definition of 'whitespace' used by the parser is slightly wider: it includes Unicode space characters on Windows and in UTF-8 locales on machines which use Unicode wide characters.