You gotta be crazy to even be considering this just to save a few bucks on data fees. Their iphone/iPad apps work pretty well. I'd stick with that if you need something mobile.
It works well on the android phones. I think the issue might be processing power though ... if something is optimized for book reading and battery life then it probably isn't a good trading choice. Frankly I won't trade with less than 2 widescreens in front of me.
The nook is a great Android device. Just install Cyanogen on it, add the nook reader if you're using it, and run the Android web of TWS. I installed Android 2.3 on a SD memory card in my nook in under 15 minutes.
Just FYI, Amazon is expected to release a new Android based tablet any day now, or before Christmas, which ever comes first.