In the Joomla! 1.6 content table there are two fields which are unused, images and
urls.
This feature uses these fields to hold JSON strings containing respectively
data on up to two images and up to three urls.
In the included layout modifications, one image is assigned to intro text for
use in blog and featured layouts while the other is assigned to the full
article layout. This is a common use case where site designers and webmasters
want to enforce a standard layout of images. Much more detailed control can be
gained by using css and overrides.
The three urls (the number is a bit arbitrary) display in a div that can also
be styled. Again, more complex and interesting layouts can be created via css
and overrides. The links have options to open in various ways that make sense
for different use cases.
In addition both the global options and the new slider contain options to modify the back end editor layout, which makes use of these options more powerful. Administrators
choose whether or not to display the articles options slider and the publishing
options slider in addition to the images and urls slider. These should work as expected (article specific settings should override global). The options to change the display of these sliders should only be available to superadmins and people with configure rights for content. Additionally, administrators have the option to enable or disable the images and urls options in the front end. Finally the global options allow a modification to the editor layout to put the editor area directly below the title if desired.

See discussion at http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=26783