I have been working on my hook and query letter as I revise my manuscript. I think that next time, I'm going to write the hook and query first, before I am mired in details from the actual work. Here are some good places for information on writing hooks:
Agent Colleen Lindsay talks about the importance of the hook--beyond getting an agent. She also links to Prince of All Agents, Nathan Bransford, and his discussion of the hook, here. Querytracker.net blogspot has examples of hooks.
Now, there are some differences in semantics in the examples above. The hook does not necessarily need to be included in the query, but it is the main conflict that can explain the selling idea of your book to everyone, starting with an agent. Querytracker explains the hook as the grabber in the query letter, and I don't see why you wouldn't put your hook in the query.
Some people call the whole query letter the "hook". There are whole contests around these 250-word hooks.
As if we don't have enough pressure to develop good hooks, Agent Jessica Faust piles it on.