Normally files are discovered hierarchically so anything in the base theme will be applied to your theme, and overridden if it's also contained in your theme.
I don't know why it's not working for the ThemeZonePreview.png, this sounds like a bug in the way the image is getting displayed and you might want to raise a workitem in the Issue Tracker.
Placement.info should definitely be getting applied and you could test this by temporarily changing one of the Place values to "-" to see if that shape disappears.
I'm not totally sure what you mean by "as yet unknown and undisplayed problems" but of course 1.1 is a brand new release and there are bound to be bugs yet to be discovered :) What are you asking about dlls in the theme?
Also what do you mean by feedback covered programatically, are you suggesting a feedback form contained within the admin UI? These forums and the Issue Tracker are the places for feedback and bug reports, I think having a system rolled into the Dashboard
might discourage people from first looking for an answer or existing workitem before reporting issues.