If we can disable notifications, then they kind of lose their function... The ratings notifications might be a bit uninformative for some, but in most other cases, notifications are supposed to be (or in my vision they are, in any case) the "summon person" buttons that you use somewhat sparingly, but which certainly are a convenient and useful tool. 
Hence, I'd rather have a system that makes you make an extra move or two to specifically notify someone over one in which you'd have to resort to PMing people old-school style because the person turned notifications off after receiving eighty-seven when they left for a family vacation for the weekend.