For a small fee, you can now get all the important features and useful apps which B&N's locked down device does not provide, including access to Google Play, other reading apps, and more. According to the hype email, you can make Skype calls using the built in microphone and use BT keyboards.
I tried one of these cards on my NookColor back in June and things did not end well. My experience was that battery life was terrible, a complaint which several other readers shared. I also had trouble getting the modified Nook Color to work consistently; over the course of a single morning I had to reboot it several times because the touchscreen stopped working.
At that time I thought that a $99 Android tablet offered a better value than a NC using one of these cards and I still think that's true.
Of course, that was an older version of the Nook2Android card, and it was also a much weaker device. The Nook HD+ is a significantly more powerful ereader, with a better CPU and all around specs. Hopefully it will perform better than what I encountered.