The first change old GNOME hands will notice is that, most, but not all of the default icon theme has been changed. Its now based on Tango.
The Tango Desktop Project is an effort to create a consistent graphical user interface across all Linux desktops.
Whats important about this, is that its working with the Portland Projects efforts to make it easier for both users and ISVs (independent software vendors) to work to use the Linux desktop regardless of whether its KDE or GNOME-based.
Thus, the GNOME Tango-based icon theme will now work with applications written for other desktops, such as KDE or XFce.