I've built a small desktop app for myself that logs listens from iTunes and Rdio so I can create powerful playlists based on how I listen to music over time, but it requires each track to have a unique ID that will never change, regardless of which app I used to listen. I currently retrieve unique IDs from iTunes using appscript in Python:
from appscript import *
it = app('iTunes')
it.current_track.persistent_ID()
However, when poking through the Rdio Suite AppleScript Dictionary I don't see any kind of unique ID attached to tracks. Suggestions?