A Snarkling wonders:
I don't know what you ask people to send with their queries (sample chapters, synopsis, etc.), but what order do you generally read them in? Do you always at least glance at the first page of the novel, even if the query letter sucks? Assuming the author hasn't totally botched it and sent you something outside your genre or also included a helpful pamphlet on why George Clooney loves them more than you, do you still take a look at the work even if the query letter isn't perfect? How lenient are you?
Miss Snark, lenient? You're pulling Miss Snark's french stockinged, stiletto heeled gam right?
The real question here is how badly can you screw up before Miss Snark gives up on you. And the answer is "good writing trumps everything". You can send me pictures of yourself snuggling with Mr Clooney, and if the writing is good enough you'll hear from me. It might be preceded by a high pitched scream, but much of Miss Snark's communications are thus.
For novels, I ask for a cover letter and the first 10 pages or so. I do read the pages. I almost always read at least three. If by page three I know this is going nowhere fast and in a handbasket, it's off to the scrap heap and a nice rejection letter "not right for us".
I don't read the stuff in areas I don't represent. They get a different rejection letter.
I completely fail to understand agents who only want cover letters. It's my experience that cover letters are not a reliable indicator of the work. Sometimes yes, but not invariably. I earn my living finding good writers, I'm not going to overlook something cause the query letter sux.
A query letter that's well written, pages that are neatly presented and correctly spelled are more likely to get a yes I'll read this than the pages that aren't. It's my experience that meticulousness in presentation carries over to meticulousness in craft. I want to work with those people. I look for those people.
Don't screw up.