Great post and thread over at Making Light on pitches and pitch scams, with a big segment on why pitching is pretty much pointless for unpublished novelists. I agree heartily, though I still think it's worth having an idea of how to do it for two reasons.
1. Sometimes an editor asks about what you write and it's nice not to sound like a babbling cretin.
2. Eventually, if you're skilled and lucky you'll be published and pitches do sometimes sell books once you've got an established reputation.
But, it's not a key skill for the beginner, and if the very thought gives you cold sweats, go over to Making Light and reassure yourself that it's not something you really need to worry about at the moment.