Google created the "Hide read labels" and "Hide Labels from Subjects" labs to help people manage their ever-growing lists of labels. Today, Google announced that they have decided to graduate these Gmail Labs features into fully-fledged features.
Google also made a few improvements to how they work:
First, instead of simply hiding all labels from subject lines, you can now choose which labels to show or hide. Also spiffed up and organized the Labels tab in Settings as well as the dropdown menus for each label in the label list.
If you had enabled either Labs feature, your settings should automatically be carried over. If there was a glitch in the matrix, or if you want to change the visibility for a bunch of labels quickly, you can adjust them en masse by going to the Labels tab in Settings.