First, these are educated guesses but those guesses could still be wrong. The Android 2.0 Feature Set:
-Contacts List gets a slight overhaul with contacts status updates via popular social networks. Its still with no eclair code drops yet still a guess and the guess is that Motorola provided the code for those features.
-Underlying infrastructure of webkit was refactored to make ti faster and allow more webview embedding via Android AppWidgets
-Blutooth is updated to include new features
-improvements in GWT support including updats to GWT 1.7.1, native json support im the RPC parser, adding more gwtorm dialects to suport more databases, and etc.
These are only educated guesses and still have a possibility of being wrong.