how was the user sure what happened before? with the old system, you were thumbs-upping a video from your google account. your thumbs ups were probably visible somewhere on youtube, and the things that you thumbed up were reported back to google and probably influenced your search results.

now, you're +1ing a video from your google account. your +1s are visible somewhere in google+ and are reported back to google and influence your search results.

it's the exact same thing, the button just looks different.