You'll potentially see two new tabs on the User Profile - "Reputation" and "My Opinion".
"My Opinion" lets you answer a series of yes/no questions regarding the user you're viewing. All questions are optional, votes are registered immediately when clicked, and can be changed at will.
"Reputation" shows an aggregate view of everyone who's voted on each question for each person, giving a high level view of the reputation of various people as it relates to the questions being asked.
Changes made on your "My Opinion" screen about someone will not update the "Reputation" screen automatically, you'll have to refresh the page to see the new values because all the tabs are loaded at the time the page loads, not when you click the tab.
The question list is flexible, items may be added or removed at any given time.
There are minimum requirements to be able to give your opinion to limit mult abuse, if you haven't met them yet you may not see that tab. Everyone can see the Reputation tab, it's public info. You can not vote on yourself. You can not see who voted on you, only how many votes the percents represent.
Mods may or may not have voting disabled on their pages, but so far are not planned to have it disabled.
You can not opt out of this feature, you can not hide what other people think of you, you can not prevent people from voting on you. Yes it's visible on your profile it's public opinion, therefore you don't own it and can't control it.