In Google+, I'm not sure who can see a comment I make on a post. Is it open to the world, or just to people that can see the original post? (I realize that the set of people who can see a post can expand over time.)
Only the people that can see the original post can see the comment.
When you +1 or comment on a post, whoever can view the original post will be able to see your +1 and comment as well.