The update dropping for the Nook Color today is the big one: It tries to take the Nook Color all the way to a full-blown tablet for $250.
With the update to Android 2.2, the Nook Color is getting a better browser with Flash support, real email and calendar programs, page-turning animations (a big deal for some people!) and yes, apps. The apps have to be designed specifically for the Nook Color, with Barnes & Noble approving every one of them—the main guidelines B&N's pushing for apps is that they're "suitable" for the Nook Color's reading-centric existence, and that they're designed for the 7-inch screen (avoiding the one of the problems that plagued the Galaxy Tab). So, think reading apps like Pulse and Epicurious (which looked pretty great) and simple games like Angry Birds. They're launching with around 125 apps today.
Real, full-blown apps might let Barnes & Noble make the argument that the Nook Color is the cheapest decent Android tablet out there—it always felt like that's where the Nook Color kinda, sorta wanted to be—but the question is if developers are going to deliver enough apps, enough stuff to make it feel like a real tablet, even considering it's only $250. (You know, if you aren't rooting it to do stuff like run Android 3.0 on there.)
To wit, today there are no Twitter or Facebook apps, much less something slightly more obscure, like an Instapaper client, even though the mix of apps is leaning more paid than free. And as more and more Android tablets show up, it might get harder and harder for B&N to convince developers to work on app specifically for its platform, since it requires some customization, not only for the screen size, but to make sure the UI is "simple" enough for the Nook Color's users. (Which is not a bad thing from an end user standpoint, given the UI on some Android apps.)