Where's the missing gigs? Hard drive mystery exposed!

The Xbox 360 ostensibly shipped with a 20GB hard drive, yet only 13GB were available for users. So what's taking up all that space? IGN breaks it down for us:
- Backwards-compatibility emulator
- Reserved space for compatibility updates
- Reserved space for title updates/patches
- An updatable "music database" containing CD and track information so you don't need to be online to properly identify and tag ripped tracks.
- And music videos as well as Hexic come preloaded on the HDD as well.
I'm curious as to how large the emulator and the music database are. What if a user has no need for backwards compatibility and has an always-on broadband connection?