Currently it's marked optional, but it's used for more than just normalizing ISBNs for Amazon cover image display, and usage will likely increase.
To say nothing of the fact that C4::Koha won't compile if Business::ISBN is not present.
Pushed, please test and close
This bug has a patch presently committed to HEAD and 3.2.x. Please take the appropriate action to update the status of this bug. Remember, bugs which have been resolved should be tested and marked closed, preferably by the original reporter.
This bug has a fix which was committed to the 3.2.x branch and released in 3.2.1. Please take time to update the status of this bug and mark it RESOLVED FIXED so that it may be closed.
This bug is mentioned in: bug 5389: mark Business::ISBN as a required dependency http://lists.koha-community.org/pipermail/koha-patches/2010-November/012916.html
This bug is mentioned in: bug 5389: mark Business::ISBN as a required dependency http://lists.koha-community.org/pipermail/koha-patches/2010-November/012915.html