With Exchange 2003 SP2 coming out soon, Sender ID will become more important. How do you set up the DNS record for the domains in your organization? You can easily do this with the SPF Record Wizard.http://www.anti-spamtools.org/SenderIDEmailPolicyTool/Default.aspx
Should a company start doing this now? Yes. Even though the Exchange's Sender ID functionality is not available for much of the public, companies are already implementing this and other technologies that use SPF records.