We decided to test the SQLite3 extension, and we also had two people writing tests for LDAP. With a nice end result of 24 tests written for SQLite3 and 9 for LDAP, we are very pleased with the result since only 9 people attended our event. Our mentor Felix De Vliegher had given us a very clear instructions and apparently most attendees already had seen my (and other people's) slides on slideshare.net. See the pictures of those great moments on flicr.com.
You can check out some of the impact that they and other TestFesters made this past weekend in the PHP 5.3 code coverage report.