In addition, the fact that I wasn't checking for errors on the rename operation allowed me to get away with not seeing a couple serious logic errors: this script occasionally attempts to rename files it has already deleted in addition to trying to rename the "." and ".." directory entries.

Updated code follows:

#!/usr/bin/perl -w

# mp3clean: make an iTunes music collection more Internet friendly.
# Micah Valine <micah@micahvaline.com>

use strict;
use File::Find;

die "Usage: mp3clean [Music Root Directory]\n" unless @ARGV == 1;

my $start_directory = $ARGV[0];

print "\nmp3clean is designed to make an iTunes music collection\n";
print "more Internet friendly by renaming files and directories in\n";
print "a more appropriate manner. Running it on a directory other\n";
print "than a directory of mp3's may cause permanent damage.\n\n";
print "Press Enter to run mp3clean on [$start_directory]. ";

my $user_response = <STDIN>;
finddepth(\&cleanup, $start_directory);
print "\nmp3clean complete!\n";

sub cleanup() {
   # get rid of these annoying files while we're at it
    if (($_ eq ".") || ($_ eq "..")) {
        return 0;
    }
    if ($_ eq ".DS_Store") {
        unlink $_;
        return 0;
    } elsif ($_ eq ".FBCIndex") {
        unlink $_;
        return 0;
    } elsif ($_ eq ".FBCSemaphoreFile") {
        unlink $_;
        return 0;
    } elsif ($_ eq ".FBCLockFolder") {
        rmdir $_;
        return 0;
    } else {
        my $original_filename = $_;

        s/\'//g;
        s/\,//g;
        s/\#//g;
        s/&/and/g;
        s/!//g;
        s/\(//g;
        s/\)//g;
        s/ /_/g;
        $_ = lc($_);

        if (-e) {
            warn "Cannot rename $original_filename to $_: file exists\
+n";
        } elsif (!rename($original_filename, $_)) {
            warn "Cannot rename $original_filename to $_: $!\n";
        }
        return 0;
    }
}
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