My first book, SC1, went live on Amazon on January 10th. It went live on Barnes and Noble only several days later, and on Smashwords only a few days ago. Thus it was far from a full month, yet I still managed to do 29 sales:
Amazon/Amazon UK: 8 SC1, 5 novellas
Barnes: 12 SC1, 1 novella
Smashwords: 3 SC1, 1 novella
I have to say, I'm surprised a bit by the numbers (especially Smashwords--the novella has been live there only since 1/29 and SC1 since 1/30). Going from zero to 29 in only 3 weeks seems like a pretty good start to me!