Chuck Klosterman has a great collection of essays on the whims of both popular and highbrow culture:
People in general are reading less fiction, but I don't think this is an intellectual decline. Many people, in the US at least, are spending more time at work and commuting; combine less free time with access to a greater selection of film, television, and video games and it makes sense.
Likewise, to answer Robert's question about young adult readers, procreation probably hamstrings more readers than anything - when it comes to reading a book by yourself versus doing something with the spouse and kids, the later is usually going to win out. In the past, the largest pool of adult readers probably consisted of housewives reading during the day and hands-off, minimal effort fathers reading at night - with cultural and economics shifts draining these demographics, it makes sense to me that more public forms of storytelling like film and television are gaining cultural currency while readership is declining.