My little 9 year old nephew got a Kindle Fire HD for Christmas and I was helping him get it set up. Man, that thing pisses me right off. No access to the Google Play store at ALL. I still have some credit at the google play store from when I bought my Nexus and I was going to purchase him a couple games he wants but you can't do it on a Kindle. Can't use the google play store app without rooting, and can't do it through the google play website either. Lame. What's the point of a Kindle being an android tablet if you are cut off from google functionality?
On the flip side, I bought my mom a new Nook HD+ for Christmas(the 9-inch one) and it's badass. Comes with Chrome as the default browser which was awesome, and a ton of useful apps preinstalled like Pandora, Spotify, etc. All that for $150 for the 32GB version.
I can't fathom why people get Kindles over Nooks(if you're going to go with an e-reader device rather than a straight android tablet). Nooks are superior in almost every way possible, you can buy books from any source, they are compatible with all file types, they aren't nearly as restrictive as amazon and their Kindles.