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, we don't notify the person that you've ignored or blocked them. (Help center articles are available at http://goo.gl/HQ7AS and http://goo.gl/KNW7L )
Google+ is the new social networking kid on the block, and one of the main reasons so many people are interested in the service over Facebook is Google+'s proclaimed focus on protecting users' privacy.