Long guns are not currently registered during the background process. However, the s/n is kept on the dealer's books. The DOJ or ATF have the ability to audit the books, but audit for compliance purposes, not for the purpose of pairing a specific long gun with a specific person.
That said, the DOJ or ATF can zero in on who a particular long gun if necessary. They do this by contacting the manufacturer, finding out who the lot was sold to, and then tracing the long gun down to the dealer level. From there, the dealer provides the record indicating who the long gun was sold to.
In 2014, the registration process for long guns will be exactly like the registration process for handguns. People purchasing long guns prior to 2014 are generally not required to register them. However, if you move into California on or after January 1, 2014, you will have to register everything. You will also be required to report intrafamilial transfers of long guns after January 1, 2014.
** This is based on my reading on AB809 and is not a legal opinion. Anyway, if you are relying on a random internet poster for 100% accurate and complete info, you aren't the brightest tool in the shed.