Genius on-the-fly playlists on iPods and iPhone? How is that possible?

I got puzzled by the addition of Genius playlists on-the-fly on the iPod/iPhone. Let's see, we don't even get "smart playlists" on these devices, so how could they be able to do the heavy computing I thought the Genius feature requires?
Well, pretty easy.
I went and had a look around my HD since I was wondering how the iPod/iPhone could handle Genius playlists without doing some heavy computing... turns out iTunes 8 creates an
iTunes Library Genius.itdb
database file in the Music>iTunes folder on your HD, then it gets copied over to your iDevices... This DB must contain lots of metadata about your songs, and when you hit the GENIUS icon on you iThing, it just shuffles amongst songs with related metadata to the on you are listening to...
In my case, the file is 120MB, for a 160GB music library...