Oooo-- we love our e-readers.
DD (11) has a basic Sony reader, the pocket edition (non-touchscreen)  That thing is a ROCK.  
I have a Sony touchscreen, which I also love, though it is somewhat more tempermental overall.  It bricks up fairly regularly and the USB trickle-charging can be fickle.  A PSP wall charger solved  that problem, however.
DH has a B&N Nook color.  It is AMAZING.  
We were given a Kindle by a family member-- and (honestly?) RETURNED IT.  The reason is that the proprietary format of materials made it an unholy pain in our estimation.
All of our devices will run multiple formats (E-PUB, PDFs, WAV, etc.) and we can check things out for free from our public library anywhere we have a wireless connection and a computer.
DH's Nook has wireless capability, which he likes.  He loves the freebies from B&N, too.
The iPads are really nifty, though.