As authors, we both love and despise feedback. We're both the most egomaniacal people on the planet, but so insecure with it. We're arrogant enough to expect people to not only read our words, but pay for the privilege and enjoy it too. Every negative review is a huge kick in the teeth. Some authors struggle over a book for as much as a decade, and it really is like a child. You just want the best for it.
So it might seem a bit counter intuitive to say, but EVERY review adds value to your book. Even those that completely slate it. Of course, this comes with a caveat. Every review is valuable if the public don't already know about your eBook.
This isn't just me making up nonsense either - Professor Alan Sorenson of Stanford University says so too. He used three mini studies in making his assessment. He looked at 244 fiction titles printed from 2001-2003 (Yes, pre-eBook, so take it with a small dash of salt!). He measured post review sales spikes. Every single book getting a good review gained. Every single book by an obscure author gained as well.
Of course obscurity is an abstract concept. The theory behind it is that reading a bad review elicits two response:
1. Familiarity - you get some brand/ name recognition.
2. A negative response in relation to the comments
You gain if the former outweighs the latter. This involves looking at decay rates i.e. how quickly these two reactions fade. What Sorenson found was that familiarity had a longer shelf life than the negative connotations that went with it. Thus, if you aren't well known you gain more.
So, can we apply this print book study to eBooks? I think we can in a general sense. If a review gets you known then it's probably a good thing either way. The downside is that as indies we don't get reviews that get the exposure of the New York Times. An Amazon review might simply be seen by a few individuals looking for an instant eBook purchase, in which case the decay rate won't kick in within the time frame and thus the negative review might just be that. A negative review on a book blog or review site on the other hand can help increase awareness, so that when a prospective customer later sees your work for sale they think "I know that guy", and thus become more likely to buy.
The other major consideration here is Amazon metrics (as well as those for the other stores to a lesser extent). If a negative review is your only review, chances are it is much more damaging. A dozen good reviews can easily temper a bad one. I know I'll disregard the odd negative review if the general consensus is positive. We all know that some users troll, and authors sometimes resort to sabotage of competitor's books (which, if this is right ironically means they're probably helping us - Obscurity is an author's real fear!).
Amazon won't penalise you too much for a few bad reviews either. Sure, you won't be right at the top if someone sorts by high to low average review, but those perfect 5 star averages never last anyway. All we can do is make sure we produce the best book possible, and target the right market to get our books seen by those predisposed to like them.
After that the book will sink or swim on its own merits.