Which firmware on your Nook (I'm assuming 1.1) and have you tried any other ad hoc wifi connect yet? And I'm also assuming you've used auto-nooter and jumped up to at least Froyo - I'm personally having a prob with Gingerbread, still have a 4gb microSD card with Honeycomb Preview 4 on it.

I've rooted my Nook, use my rooted Captivate as the wifi hotspot, I don't see any slowness. I've unfortunately gotten rid of my N900, but just wondering if you could test anything else. I've noticed that Froyo on the Nook is just plain slow in some areas - browsing one of them.