HUBZone Improvement Act of 2008 - Directs the Administrator of the Small Business Administration (SBA) to: (1) correct and update the map used by the SBA to identify HUBZones (historically underutilized business zones) and to ensure that it is updated on a more frequent basis; (2) develop and implement guidance for determining whether an applicant is a qualified HUBZone small business; (3) establish a date for elimination of the backlog of applications for recertification as a qualified HUBZone small business; (4) ensure that the SBA eliminates the backlog by such date; (5) establish and implement a time period for completing a recertification; and (6) develop and implement plans to assess the effectiveness of the HUBZone program.