Young Adult Series Trend

The biggest trend that the entire publishing industry seems to have embraced is the young adult series'. Fantasy series seem to be the favorite. Maybe since youth have great imaginations, I am not sure.
Here is my observations. I distinctly remember my parents mentioning Harry Potter as is was just beginning to gain momentum in the US, and I thought 'why are they so excited about a kids book'. Then they went on and on about how I needed to read the book, so I did. Needless to say, we all would go the first day or pre-order the books as they were published. We had to each get our own copies since no one wanted to be the poor schlup who has to wait until everyone was finished to read the book.
For me, and the rest of the book world it seems, that was liberating. Not only have I picked up many more YA books and series, authors were able to write to that audience that was youth, crossed over to adults. The YA genre is one of the biggest requests that we receive from Ijustfinished.com's reviewer profiles. Not only that, it is an almost sure fire hit for publishers. Many of the series have such a loyal following, that people (note I did not say kids) pre-order and line up for the next in the series. To follow that up, they seem to translate to the big screen quite well. Many YA series have been become movies. Many successful movie series actually started as successful book series, including "The Princess Diaries" by Meg Cabot, and of course the latest due out this Dec is "Twilight".
That brings to mind the down side of the trend. Series are nothing new, even the James Bond movies that are books first and then became movies. The pressure to continue characters and story lines has to be difficult, but keeping YA readers happy is a challenge in itself. Teenagers are a fickle bunch anyway, and just in the way that characters evolve and grow and present themselves differently through their experiences, so does the YA demographic. I clearly remember the tone and mood change of Harry Potter in book 5, when he became a full blown teenager. He was darker and more brooding. As an adult reading, you know that is part of the process, but as a teenager, that might be enough for them to put the series away. That pressure has to be tough, along with the leaking of plots and rumors of story lines.
The great thing about the trend, however, is that it allows for the most creative worlds, and stories. Marie Rutkoski author of "The Cabinet of Wonders" dropped by 'Coffee with an Author' a few weeks ago, and the world she created is so original and creative that it takes you back to childhood. Maybe that is the attraction for those of us adults that enjoy YA so much.
I really hope this is a trend that finds a permanent place in the publishing industry, and doesn't flicker out.