Assertion:
Netscape DOES seem to allow the DEFAULT value for the SHAPE attribute, but appears to require that it be placed at the END of the list of AREA elements. If it is not, the HREF for the DEFAULT area shape will be used for the entire image. Opera appears to allow DEFAULT as a SHAPE attribute value anywhere in the list of AREA elements.

Image map (#imgmap1), with no DEFAULT area:
filler text filler text

Image map (#imgmap2), with DEFAULT area first in image map definition:
filler text filler text

Image map (#imgmap3), with DEFAULT area last in image map definition:
filler text filler text

Shape destinations on image, no default destination:
ShapeURL
http://www.yahoo.com/
http://www.google.com/
http://www.blooberry.com/
http://slashdot.org/
arealocaltest.htm