In general, my thoughts would be:
1. Edits should be clearly communicated to the reader somehow, as with a "version" number. Many sites don't support that -- perhaps a page at the back to clarify (a) what version the file is in and (b) the version history info? Add an email address -- if someone doesn't like an edit and wants their older version back, you have an opportunity to work with them.
2. Every book could be tweaked for eternity, and as an author, you MUST stop, draw a line under your work, and move on to the next one. On the other hand, I just read an indie book yesterday that had great potential, but I felt failed on the execution. Since the point of that novella was to drum up publicity for the "real" series for sale, the bad writing could hurt the author in the long run. So I think there's room for a cost/benefit analysis: Is the book selling well and getting good reviews? If yes, leave it alone. Or are you getting, "Eh, could be better written" reviews? In that case, IF the book in question is meant as a "gateway" book to a bigger series, you might edit it a bit. If it's a standalone, there may be less potential pay-off.
Hmm. I had more thoughts, but they evaporated while I was pontificating.
