That Slushkiller post is great and helped boost my confidence when I was in the query trenches. If you've written a complete, unpublished book and followed the submissions rules you're already doing well. And definitely don't read too much into the agents who don't respond at all. I sent out ~80 queries over the course of a year before I got my current agent, and from those I had about a dozen requests for fulls and partials, two offers, and about 30 non-responses. One agent took a full eight months to send a rejection, and I've heard of people waiting a lot longer than that.