Right before a major release they do a public testing phase for new and improved games, which helps them iron out any remaining bugs. This testing cycle includes two new games: Myst (and Myst: Masterpiece Edition) and U.F.O.s (also known as Gnap). There also have been a lot of improvements in the SCI engine as of late, so they are also testing Conquests of the Longbow, Freddy Pharkas: Frontier Pharmacist, King's Quest V, King's Quest VI, Quest for Glory 1 VGA, Quest for Glory 3, Space Quest 1 VGA, and Space Quest 4. Other games that have seen recent improvements and are undergoing testing include Beneath a Steel Sky, the Commodore-64 version of Maniac Mansion, Sherlock Holmes: The Case of the Rose Tattoo, and Sherlock Holmes: The Case of the Serrated Scalpel.
So, if you have any of those games, play them through in a daily build of ScummVM on your platform of choice, and report any bugs you find at the new and improved ScummVM bug tracker. Then tell the team about your experience, and any bugs you filed (or if you didn't spot any bugs at all) in this thread on the ScummVM forum.