The good thing about the sideloading solution Penny pointed out is that once you make the minor mod to the stock firmware, your Nook HD/HD+ won't even have to sideload most apps that Google Play previously "hid" from the device due to hardware limitations. Almost all of them now show up in Google Play as compatible with your device and you can download them normally. So you don't even need to get APKs to sideload.
USA Today, Yelp, NBC News, TV Guide ... all these apps I couldn't download before the mod but now show up normally in Google Play. Interestingly, the only exception to that is Amazon Local. I don't think there is anything intentional there since Amazon Mobile shows up fine. Must just be something quirky. So Amazon Local is the only app I've had to sideload.
Bottom line is the mod not only allows sideloading of apps, but it tricks Google Play into thinking your Nook HD/HD+ has more hardware features than it really has!
--Pat