Our private K-8 school is exploring use of Kindles. My daughter is using one due to her broken arm, to reduce the weight of books in the backpack. The DX (larger screen) version easily accepts PDF files as well as Kindle books, so it seems a good choice for student use. Downloads are quick and simple. E-Ink screen is very easy on the eyes (including in the car). Automated voice is good, though not in the range of the professional audio book readers.
It sounds like a good tool to use, but given that you could probably buy a mac mini or decent laptop/netbook for the same money, I doubt that our district will be putting much money that way in the future. Still, that said, I will be interested in any replies you get.