I'm resurrecting this old thread because when I read the 2009 Southwest Airlines annual report, it says the following on page 4:

During 2009... Improved Baggage Tracking. The Company also introduced on-hand baggage scanners, which provide Customer Service agents (i) visbility to bags in the Company's possession across the system, (ii) increased efficiency and organization with the automation provided by the scanning equipment, and (iii) the ability to recover misplaced bags more quickly for Customers and provide information as to the timing of bag returns.