I haven't found anything on the 'nuances' yet, but the
wikipedia article is a start, and then the
developers intro page starts to make some sense. Linux Journal had an article way back in March 2008 which may be somewhat dated now.
It looks like a modified Linux base (no X11, different libC) using a custom Java VM and custom class libraries. Obviously the phone control can be pulled out to give us netbooks and e-readers...
Some days I feel like I'm getting too old to keep up with everything - I used to try.