Current

• clean_up_google_music - Lets the user choose what types of items Google Music displays in the default pane - albums, playlists, suggested albums, user-defined instant mixes/radio stations, and/or auto-suggested instant mixes/radio stations. Also makes every item a uniform, smaller size.
• show_saved_searches - Shows the saved searches as a card in the main G+ stream
• show_all_pages - Increases the vertical height of pages scrollable area in the G+ account button dropdown

In a holding pattern

• hide_posts - Adds a close button to each card to hide posts from the user without forcefully muting them. With the new G+ layout (summer 2013) which added two- and three-column layouts, I'm unsure if this is still as useful as when every post was displayed in one column.

Obsolete

• no_maximize - G+ now fully hides the maximize button by default