I'm in the same boat... I was looking at the nook for some more speed, a nicer screen over the 505, but still retaining that clarity over the 900.
The 900 and 505 still beats the nook hands down for me. Just too much futzing around in menus to get where you want. More than the 505 even (without hacks). And then it requires you to get the screen powered back up to do anything, which drains the battery (especially when reading periodicals), and doesn't always want to power on by tapping it.
That said, I'm not in a huge need for wireless on every reader I've got, so the UX is kinda key for me. And the more I played with the nook, the more I realized how long the interruptions to reading were to bookmark, highlight, switch back to the book I was reading after finishing a newspaper, how frustrating reading a newspaper was, and so on.