In iTunes, is there way to switch easily back and forth between tracks in two different playlists or library parts (say podcast and music)? Use case: I often want to toggle between a podcast and a music playlist in iTunes. Say, while ironing I listen to a podcast, later when I do computer work I switch to music, then when unstacking the dish washer I want to go back to the podcast and after this, music is on again, etc, etc…

Is there a script or plugin for iTunes, which remembers track, position and library/playlist, so that I can switch back to it? Or is there another convenient way to achieve this?
It sounds like you are referring to something like a Smart Playlist. Smart Playlists organizes your songs more, based upon song type, last listened to, skip count, etc.

http://support.apple.com/kb/HT1801