I think we need to change content types to node types because the settings in them are all about how the nodes are displayed and handled by the system, not actually about the type of content in the nodes (which would be rather a semantical thing).
I think the blog node type needs some re-thinking. I think it would be great to be able to add any type of node to a blog. Instead of making a separate node type for blog posts, they should have a checkbox whether or not they are on the /blog page of the author (actually much like the book module, but simpler).
Polls should be a separate node type, no doubt. The functionality of polls is so different from other types. Same for 'Issues' like they are used on this site. However, I am even wondering if it would make sense to make forum topics a custom content type (much like what happened to book pages in D6). There is nothing about them that makes them fundamentally different from plain node types, just the framework around them. I think the forum is more defined by the way the topics are structured than the way the content type is designed.
Thinking this through, a few examples: