"In my experience most people who follow the big fad of the day (royal wedding, big brother, american idol, etc) are never really fascinated by it. If you ask them "what fascinates you about american idol?", the answer you're most likely to hear is "wtf, what do you mean?". Many of these things are designed to be attention-grabbing and to encourage chattering about their consequences, even if there is absolutely nothing interesting or actually at stake in that."Hmm, my experience is quite different here. Generally I find that people may start off with some big fad of the day because it's nominally a 'safe' topic and something which can start a conversation without offending or knowing another persons interests apriori.
Almost any 'fad of the day' topic has a route into a more interesting topic.
American idol - influence of music on society, what defines popular, changes in the music industry that make idol possible, etc.
Royal wedding - the role of the monarchy in modern nation states, the role of weddings in changing fashion, is marriage as a concept out of date, etc.
Big brother - voluntary surveillance vs involuntary, peoples behavior when they know they are being 'watched' vs not being watched, the role of 'reality' tv in the definition of morals in 21st century society.
One of the things that can trip up folks is concluding that because someone just asked you your opinion on last night's American Idol decision they believe that the best use of your time would be watching American Idol. Take it as the equivalent of 'nice weather we're having today isn't it?' and you can often find a common discussion ground at the appropriate level.