When you mouse over the button, Google shows a list of friends that +1’d the page. The same list is now displayed next to the button if you change the code and select inline annotations. This is the new default option when you generate the code, but not everyone will like it because it takes a lot of space. Google probably chose this option because you’re more likely to +1 a page if some of your friends already did that.
The Google +1 button also lets you share a page to Google+. After clicking “+1”, Google shows a box where you could enter your comments and choose one or more circles. Google shows a title, a thumbnail and a short snippet from the page. By default, they’re automatically generated, but developers can explicitly annotate the page using the schema.org microdata or the Open Graph protocol, which is also used by Facebook. At the least, you should add a tag for the image that best represents the page.