"BIND version 9 is a major rewrite of nearly all aspects of the underlying BIND architecture. Some of the important features of BIND 9 are:
DNS Security: DNSSEC (signed zones), TSIG (signed DNS requests)
IP version 6: Answers DNS queries on IPv6 sockets, IPv6 resource records (A6, DNAME, etc.), Bitstring Labels, Experimental IPv6 Resolver Library
DNS Protocol Enhancements: IXFR, DDNS, Notify, EDNS0, Improved standards conformance
Views: One server process can provide multiple "views" of the DNS namespace, e.g. an "inside" view to certain clients, and an "outside" view to others;
Multiprocessor Support
Improved Portability Architecture"
You can check the relevant links here. There is also a history of changes (since the last beta and during the full beta period).
