Well, I can only speak for the stores in the area I have lived most of my life. Mainly the B&Ns I have always been around are uppity and snobby. They've always portrayed themselves as "better" than Borders and the customer base inside acts that way. Even though I own a Nook I have still gone to Borders for hard copies of books unless I absolutely had to go to B&N. I typically just don;t like their stores, their attitude, the layout, etc.
I always enjoyed Borders. It was more laid back, the staff were always friendlier and I even liked the little things like the computers they had set up so I could look my own books up (something B&K still doesn't do. I hate asking for help at a B&N because 1) I am more than capable of looking up a book on a computer screen and 2) they tend to make me feel small as I have to sit there and wait for them to tell me "what to do". Oh and I've received dirty looks for sitting in their chairs or at their tables and skimming a book before.
Overall, Borders here in MI were friendlier, less snobby and much more "hands-off". They let me be to explore but were there if I needed help. Every time I go into B&K I pretty much just want to get whatever it is I need and leave as soon as possible.