Visual voice mail, trackball comparisons, text message threading, and more. I think I’ve got about two more of these coming, and then we’ll move on to the in-depth camera and browser videos.
EDIT: You can sync individual groups in the people app, as per David’s comment below. But I don’t know if un-checking “sync all contacts” there effects the sort of global Android sync, or just the manual sync in the people app. I will look into it.
And here are the G1/Sprint Hero comparisons requested by @Breon: