The CSS has been reorganized: typography and layout styles reside in their own files, while color, borders, images and other "branding" elements are still in style.css.
Now it's much easier to customize and build upon Barlow without touching the original files:
create a subdirectory of the theme
copy the style.css file inside it
change the first two lines, which includes the layout and typography styles, to point to the parent directory by prepending "../" to the path
tweak the rest of the stylesheet as much as you like
The 2.0 release introduces a new localization engine for user strings, like menu title and description, taxonomy title and description and so on.
It provides also some API that can be used by external modules.
The structure of the module has been rewritten with a main module and specific submodules.
No patches to the core are necessary.
This release adds support for internal URLs, as discussed http://drupal.org/node/87311. Internal URLs are simply of the format 'node/1111' or anything not beginning with a domain (example.com) or protocol (ftp://example.com).