I had a few problems during conversion. I could see that the database text encoding had changed (at least, the sample pieces of text I was checking had changed appropriately), but UBB was still showing diamonds.

I eventually tracked that down to the fact that UBB was using the PHP/MySQL client default for character encoding, which was ISO Latin 1. I changed the "connect()" function in the "libs/mysql.inc.php" file so that if it does have a valid database connection, it sets the character set to utf8. That corrected the issue for me, so you may wish to add that change to the codebase to ensure that the character encoding is what is expected rather than relying on the default being correct.

For reference, the change was:
PHP Code

--- mysql.inc.php.bak   2015-01-27 07:05:08.000000000 +0000
+++ mysql.inc.php	   2015-10-12 08:06:30.000000000 +0000
@@ -25,6 +25,8 @@
 
		if( ! $this->dbh ) {
			$this->not_right( "Unable to connect to the database!" );
+		} else {
+			mysql_set_charset( "utf8", $this->dbh);
		}
 
		if( ! mysql_select_db( $config['DATABASE_NAME'], $this->dbh ) ) {

Last edited by Pak Chan; 10/12/2015 6:00 AM. Reason: Moved comment to later