Late to the party...
Anyway, I loaded my novella up to Amazon, Nook and Smashwords.
I use scrivener and it does a great job into compiling the work into a MOBI and EPUB format. Sometimes you'll see the odd format blurp, like an extra blank line or something... but generally those two come out pretty well.
Smashwords... well, you dump your text file into their "meatgrinder" and it converts the file into all the formats they use... I've been extremely underwhelmed by the end results.
As for sales, the vast majority of mine have come from Amazon, maybe 10-15% from Nook... and not a darn thing from smashwords. I'll still load to it, but basically as an afterthought.