Google+ now lets you ignore or block a person you just don’t want to interact with. Wonder whats the difference? Ignore means you’ll see less of what a person is sharing (i.e., you’re just not interested). Block additionally limits the ways a person can interact with what you’re sharing (i.e., you don’t want anything to do with them). And in either case, they don’t notify the person that you’ve ignored or blocked them.
By ignoring a person you will remove his posts from your “Incoming” stream, you will no longer get notifications about his activity and ignoring someone will remove him from your Circles page. If you want to ignore several people that have added you on Google+, you can click the new Ignore all button in the Notifications menu to ignore them all at once.
Ignoring is different than blocking, though. A person can still see your stream and comment on it if you’re ignoring him. Blocking him will eliminate his posts from your stream, remove him from your circles and block him from seeing anything you post.
Source: Olga Wichrowska’s google+ post