From the article:
3. When you tap on the Playlists section (should be empty at first start-up), it’ll ask you if you want to sync your playlists with iTunes. Choose yes. If you dont see it, just head into doubleTwist -> Preferences -> Library and set it yourself. It should populate with your playlists from iTunes, like the screenshot above. Might have to restart doubleTwist or give it a couple minutes if it doesnt happen.
Read on in the full 'how to'.
Me? My music collection is too large to fit on my phone's mass memory or memory card, so I normally hook up via 'mass storage' mode too, but drag over just a selection of music sub-folders from my iTunes folder tree on the Mac. One 'refresh' of the Music Player library and I'm sorted. How do YOU sync music back and forth to a Symbian smartphone?