Similar to how 2.3 overhauled the tagging, category and classification system, version 2.5 of WordPress will overhaul the admin area.
More than just a visual overhaul (which was needed), WordPress 2.5 will feature better admin functionality and an improved user interface thanks in part to Happy Cog.
The features that worry me the most are:
I’ve achieved all of those using plug-ins and custom PHP files. Seeing that list of features makes me wonder how it will affect my plugins and if I’ll need to re-do several sites to support the “out-of-the-box” features to stay compatible with WP 2.5.