These instructions are for a Nook Color 1.4.3, It may work on other Nooks, feel free to comment if it differs on your device.

First, Press the “n” key, and press apps

Press the Volume up key and the “// Library” logo at the top of the screen, you should move to the “Extras” page.

Press “Nook Color Tools”.

Double check the “Allow Non Market Apps”

– From here, I was able to download an APK via DropBox, and install it… No more installing APKs via ADB 🙂