I understand some mistakes will get through - they even creep into a few classic titles when they get converted. But sometimes they have so many punctuation errors I want to scream.
I try not to hold it against the author when I review the book, especially if I am enjoying the story, because there is no way for me to really know if they don't get it, if there was bad editing, or if it happened during formatting. Also, I am not the comma champ myself.
The book I am currently reading though - I just hit a chapter that's like William Shatner and Christopher Walken had an argument over where the pauses should go, and ended up having a comma fight where they just threw handfuls of them at each other.