For 1.0, what would you like to see changed or included in the "easy to use" API for creating your own extensions?
I think it's fairly straightforward and works well right now but the biggest change I can see is making extensions easier to distribute.
What I'm thinking, is that rather than a local_feeds.inc.php we'll do two things:
1: extensions/
Extensions would be placed in the extensions subfolder, rather than piled into a single file. This will allow you to easily distribute your extension as a zip file (folder->extension.php+icon.png).
2: themes/
All of the pages which are rendered (outside of the admin) would be stuck into a themes/default/ directory.