With the recent announcement that IANA has allocated its last remaining IPv4 address space to the Regional Internet Registries (RIRs), time is running out on availability of new IPv4 address space allocations. As the last remaining IPv4 address space is allocated, enterprises at some point in the not too distant future will have no choice but to implement IPv6 for Internet-accessible web or email servers. Any newly-formed organization or those that require additional address space after this time will be "IPv6-only" organizations.
Perhaps you're thinking this is not an issue given the plentiful private IPv4 address space. But consider this: as this population of IPv6-only organizations and users grows into 2013 and beyond, will they be able to reach your websites and email? To serve this population which will grow rapidly as more IP-based public and private applications are deployed, implementation of IPv6-addressable Internet servers is imperative.
Besides implementing IPv6 on Internet-facing servers, enterprises should take heed regarding IPv6 addresses already in use internally. Many popular operating systems including Microsoft Windows and Linux natively support IPv6 addressing. A major feature of IPv6 addressing is address autoconfiguration, which enables a device to identify the subnet address to which it is attached by virtue of router advertisement messages and to append its self-derived Interface Identifier to this subnet address to fully compose a unique IPv6 address unbeknownst to network administrators.
Autoconfiguration may provide a convenience for users initializing on a network, but it runs counter to network admission control (NAC), a strategy for reviewing and approving the assignment of addresses to devices. The scope of autoconfigured IPv6 devices can be constrained to a local link by disabling the autoconfiguration option in router advertisements or by disabling router advertisements altogether until you consciously deploy IPv6 on the given link. Take control and implement IPv6 on your terms...but do plan to implement it!