What is the significance of the broadcast address?
The broadcast address signifies "everyone" on the network. So, in other words, every network device will listen for packets destined for its assigned IP, as well as any packet destined for the broadcast address.
It is used for various things, one example is ARP requests.
See the RFC <A HREF="http://www.ietf.org/rfc/rfc1180.txt?number=1180">TCP/IP Tutorial</A> for complete information.