Honestly, I used it for the same thing I have used my Droid on occasion. A few months ago, one of my kids asked me how a tree is made into paper. I knew we didn't have any books on the topic, so I found a YouTube video for kids, a la PBS-like, that shows how trees are made into paper. He sat to the side and watched the video a couple of times and then started to explain the process to other kids. Every once in a while after that, he would ask to watch it again.
Interjection: I prefer allowing him to watch an educational video on my small Droid than to have broadcast it on that ginormous monstrosity known as the SmartBoard. That way, the other children were able to continue on with their work without being disturbed.
A few weeks ago, I managed to actually locate a children's book about how trees are made into paper. I handed it to the boy, who immediately looked through it, and then he put it in the book area. The other children have been reading it for the past several days.
Yesterday, one of the girls asked me if she could watch the video, also. Voila - a chance to pull out the Kindle Fire. The screen is larger, so it was easier to see what was going on. I pulled up the video and she sat with the Fire in the rocking chair, watching it two times. The first boy asked if he could use the Droid to do the same. A small group formed to watch the video and then to discuss what they had just seen. And then they returned the technology and went back to their works.
Actually, some of them started to create their own science experiments, but that is another story.
I know I can also use the Fire for showing some sight word books to mix it up for the kids. I have already been doing that on the laptop here and there. I will never replace real books in my classroom; but, I think I can implement a little technology and be okay.