Straight from Dell:

Dell has identified a potential issue associated with certain batteries sold with Dell Latitude™, Inspiron™, XPS™ and Dell Precision Mobile Workstation™ notebook computers. In cooperation with the U.S. Consumer Product Safety Commission and other regulatory agencies, Dell is voluntarily recalling certain Dell-branded batteries with cells manufactured by Sony and offering free replacements for these batteries.  Under rare conditions, it is possible for these batteries to overheat, which could pose a risk of fire.

Of course, if you have a laptop that is affected by this, do everyone a favor and get the battery replaced. :)