I have an Amazon thread in the Kindle Forum called "Indie author vs. Major publisher," in which I compare my monthly sales versus what I think I am selling through NY--not that NY is doing such a hot job of it...
I sell about five copies a day each of my novels and one to two per day of my story collections, with some highs and lows. It stays pretty steady, for the most part. But part of the problem with having a publisher is you really have no idea what's going on, and you just get whatever numbers they hand you. Personally, I have found the lack of control is a good trade-off for not having my books flooded on shelves for 30 days.
Scott Nicholson
Haunted Computer