Update: David Chartier points out @chucker‘s instructions for adding a track to an Up Next playlist with a keyboard shortcut. Huzzah!
Apple has released iTunes 11, which offers a major redesign of the decade-old media player/store. Alongside the visual changes are some clever features, including Up Next. Up Next lets you create an on-the-fly playlist, determining which song follows which during playback.
There are several ways to add to and re-arrange an Up Next playlist. Here’s how to work with Up Next playlists in iTunes 11.