Hyperbolic Software has updated iTunes Dupes Barrier
an iTunes utility, to version 1.2.1. The upgrade fixes
incompatibilities with iTunes 8.

iTunes Dupes Barrier allows you to search the duplicate songs inside
the iTunes and iPod songs’ databases. It requires Mac OS X 10.4.0 or
later and iTunes 4.0 or higher. It costs US$10, but version 1.2.1 is
a free update for registered users.