Filter out the free Nook books from Smashwords.
The free Smashwords books on the Barnes & Noble site are redundant and there are so many it makes it hard to find books that are just offered by B&N. Since Smashwords books are multi format and thus not just for the nook it is better to leave them in their own section.
Y.C. Haug commented
Make Smashwords a separate search from the rest of the free listings!