There's been no official announcement, and it doesn't appear to add any new features ( for example you still cannot sideload apps). The update is being distributed on a rolling basis, and was it actually started being sent out on Monday.
So what did the v2.1.1 update add? Not much.
According to my sources at B&N, this update mainly added minor bug fixes but not any new features (other than the ability to sideload comics). And according to a discussion thread over at MobileRead:
The main fixes seem to involve a comic book reader and Google Play Music, from what I've read.
I only got the update today. If you haven't received it yet and you don't want to wait, here's how to download it:
Or to get the software update right now, be sure you are connected to a Wi-Fi hotspot, tap the Settings icon in the Status bar at the top of your screen, tap on All Settings, then tap on Device Information, and check to see that your Software version matches 2.1.1. If it does not, tap on Software version and then tap on the Check for updates button. Follow any on-screen instructions. Do not turn off your device while it is downloading or installing a software update.