What's new: Now RFC 822 compliant date formatting is the default. You can go back to the old MoveableType style dating by setting:
my = 0;
Also perldoc style documentation has been added.

Known Issues: Plugins that provide their own entries routine and do not return the story files in the %files hash will cause lastbuilddate to find no date. In this circumstance lastbuilddate will not emit a field. To work around this, rename lastbuilddate so that it executes ahead of these plugins. For example, rename to 00lastbuilddate.

Download lastbuilddate here.