When you mouse over the search result, the +1 button appears.
I now see this, but not everyone sees it yet. It seems to be a test Google is trying out or maybe something they are rolling out.
Here is an animated gif of the mouse over affect.
Then when you click on the +1 button, it will highlight blue.
As I mentioned, I like this - it declutters the user interface and makes things a lot cleaner for the searcher.
Forum discussion at WebmasterWorld.