This afternoon I posted beta-4 of Email Users v4.8.5.  This build adds some additional debug information to help chase down slow database queries.  When in debug mode, Email Users will now report information about the query like this:

<!-- email-users.php::1391 -->
<!-- email-users.php::1410 Query #1 Memory Usage: 15.75M -->
<!-- email-users.php::1415 Query #1 Execution: 0.30101704597473s / 301.01704597473ms -->
<!-- email-users.php::1410 Query #2 Memory Usage: 20M -->
<!-- email-users.php::1415 Query #2 Execution: 0.29001688957214s / 290.01688957214ms -->
<!-- email-users.php::1410 Query #3 Memory Usage: 24.5M -->
<!-- email-users.php::1415 Query #3 Execution: 0.201012134552s / 201.012134552ms -->
<!-- 1282 -->
<!-- email-users.php::1448 -->