Several things rip me out of a good story, which in and of itself is a pet peeve; however, typos top my list. And while I might expect to see a few typos in a self-published work, I tend to expect more from a bestselling author and/or well-respected publishing house. Now, I'll be the first to admit my work is not 100% error free. Without fail, a few things always sneak by me in the proofreading process, things that are painfully obvious once I've sent something for publication consideration or published something to my blog. I read my work aloud, which helps to some extent. Additionally, I've also asked peers to give my work a read. To this end, I believe being part of any writer's group is quite valuable. However, because I often feel like a complete letch for asking a peer to give up his/her time to read my work, I've also considered purchasing a Grammarly membership. Grammarly is an online grammar checker that, unlike basic spell check, actually evaluates advanced grammar rules.
Another writing snafu equivalent to a punch in the face is a glaring fact error. For instance, if I'm reading about a former Navy SEAL, please don't call him a jarhead (a Marine nickname). Of course, this only applies if I know the subject matter. This said, the best way to combat misinformation is to research. In addition, if the work involves something quite specific, find a subject matter expert and run your research by him/her. There are many bloggers whose knowledge rivals that of scholars, and they are often eager to share their knowledge.
Further, if I'm picking up my dictionary more than I'm reading your book, there's a problem. I do not consider myself vocabulary challenged. And I do enjoy learning new words. Yet, it is infuriating to read an author who seeks to validate his/her MENSA membership with his/her writing. Let's face it, the majority of U.S. adults read at an 8th to 9th grade level (no, I didn't make this up, see http://askville.amazon.com/average-reading-grade-level-United-States-verifiable-statistic-source/AnswerViewer.do?requestId=9491858). Challenge me a little, but don't overdo it. As such, I tend to stick to my own vocabulary databank, incorporating new words I find powerful, amusing, or interesting. But in no case do I mistake the use of big, tedious words for good storytelling--if you care more about sounding intelligent than crafting a good story, your readers will notice.
Similarly, I also cannot stand unvaried language. I've read authors who cling to the same verb throughout a chapter. If I'm counting how many times something has been immolated, for instance, I'm no longer in the story (and I'm likely cursing you). To this end, I try to vary my language, and if I feel I'm using a verb too often, I'll search for it, making changes when necessary.
Well, now that you know I'm a completely anal retentive reader, on the lookout for typos, factual inconsistencies, overtly academic vocabulary, and repetitive language, I guess I'm done.