I put my query letter up on Nathan Bransford's query critique forum and got some really excellent advice on how to shape it up. http://www.nathanbransford.com/
I highly recommend this for anyone who has sent out a few queries and not gotten any bites. It's one thing to see what other people have done and model after them, or see what mistakes they've made and try to avoid them. It's antoher thing to actually do it. I also feel that this query thing is very subjective. What appeals to one agent, may really bother another one. Therefore, I'm trying to keep the essentials of my query the same, but customize it based on what I can find out about agents.
Anyway, it's amazing the responses you get when you seek feedback. I'm overwhelmed by the time and care these people seem to put into their responses. I'm trying to contribute to the community by making my own suggestions for people, but I don't feel like I'm very good at it. It is really interesting to see what other people are writing though.