If you haven't noticed before, there are a lot of trends in the book world. For six months a certain genre or idea for a novel will be very popular with bibliophiles, then it will shift to another.
In no other super-genre (it's not a regular genre--it's far too big for that) is this more true that Young Adult Fiction. Literary fiction comes in at a close second.
Let's look at this closely: when Harry Potter was king (and to me it's still fresh in my mind) there were tons of traditional old fantasy novel. And now, when Twilight's king, there is no end to what the vampire world will see. I can't imagine what way they'll find to take a classic creature, ruin it (or as they call it putting a "twist" on it) and make a girl fall head over heels for it.
But you can tend to notice a pattern with this. There's that one breakthrough novel, that one really good book that everyone wants to read and is many times excellent in writing and plot and description (exception, of course, being Twilight, which has garnered popularity through flowery writing people say is "good" and a "hot" male character). And the rest of books that go with this trend are usually low-quality, B-grade books or below.
The question that this gives is that as a reader or writer, what do you want to be: someone who makes a new trend, or one who follows another popular author to ride on the coattails?
By rule, a person who sets a trend has to go out of the current comfort zone and read what no one is really read about. This means risk. This means you might have to even self-publish or read books by authors no one has ever heard of.
Or you could be a trend follower, swinging along with whatever's going along.
Neither of these are always right, neither are always wrong. If what you legitimately want to read or write is not the norm right now, do it anyway. This is how all the trends we see today are set. If your passion leads you to somewhere that appears to be overdone, there have been great successes for revitalizing a genre that was once thought to be dead.
So just think about it when you next walk into the Barnes&Noble nearest you or sit down in that good-old Starbucks to pen the first words of your next work of fiction. Think about what you're going to do with what's out there, and you may end up setting the next trend.