National Guard and Reservists Debt Relief Act of 2008 - Amends federal bankruptcy law to prohibit the bankruptcy court from dismissing or converting a case based on means testing while the debtor: (1) is either on active duty in the military service of the United States or performing a homeland defense activity for at least 90 days, and during the 540 days following the end of such period; and (3) was called to such active duty or performed such homeland defense activity after September 11, 2001, as a member of a reserve component of the Armed Forces or the National Guard.

Directs the Comptroller General to study and report to Congress on whether and to what degree members of reserve components of the Armed Forces and the National Guard: (1) avail themselves of the benefits of this Act; (2) are debtors in federal bankruptcy cases substantially related to service that qualifies such members for such benefits of this Act; and (3) are debtors in federal bankruptcy cases materially related to such service.

Requires such study to include the effects that the use by such members of this Act has upon: (1) the bankruptcy system; (2) creditors; and (3) the debt-incurrence practices of such members.