I notice that my B&N rankings seem to be slipping, even on my book that's still selling well over there. It sold 165 copies yesterday, and yet it's ranked over 1100. Weird, as I'm pretty sure that used to be enough to get it up into the 200s range. My guess is that there are a lot more books selling really, really well in the Nookstore-- which is good news for all of us, I think.
Also, in the "what sells well on B&N does not necessarily sell well on Amazon" category, that same book has sold a big two copies so far this month on Amazon.