What I do is try to "calibrate" the reviewer.
If a reviewer regularly rates something close to how I would rate it, then I will be happy to rely on that reviewer's opinions.
If I find that I regularly disagree with a reviewer then I conclude we have different tastes.
I am new to the kindle and I was trying to calibrate the reviews on the kindle store for new or kindle only books.
At this point, my conclusion is that they are not reliable.
When I see an author posting a 5-star review for their own book then I strongly suspect they're boosting the ratings.
see here
http://www.goodreads.com/book/show/5...ight_in_Madrid
and here
http://www.goodreads.com/book/show/6...Takes_the_Cake
The other point is that if the download is $0.0 then I can't rely on the download numbers as there's no risk for the downloader.
I am not saying the books referenced are necessarily bad books but if the author lacks confidence that others will give them good reviews that can't be a good sign.