From the Good E-reader Blog comes this disappointing news:
Barnes and Noble has closed a loophole in the Nook Tablet that allowed users to sideload in their own applications, bypassing the official app store the company runs. Recently the company released the new 1.4.1 firmware update for the Nook Tablet and it carries with it the inability to load in your own apps. Before this update dropped, it was possible to load in your own applications via the web browser. You could simply click on a APK file and it would self-install to your device. You would then get a prompt asking you if you wanted to install it and then after selecting yes, you are good to go.
This is sad because the B&N store has far fewer apps than any of the other android app stores.