Corey, to answer your questiion: AMCs control much of the business now as regulations have forced mortgage company to play round robin when it comes to assigning an appraiser to a particular property. In the past, a mortgage company could go direct to an appraiser but now it seems they have to go through the middle man or woman (AMC). AMCs take a huge chunk for themselves (often half). This is not to say that you can't make it as an independent, but its in the lender's best interest to use an AMC that will do field reviews on all these orders, as opposed to going with a mom and pop that may or may not know the markets well enough and will return values that are too high or too low.
I'm planning on taking the appraisal course, mostly because i know i'll be making a little more than i do now, completing Broker Price Opinions (BPOs). Some can be a piece of cake, while others will have you pulling out your hair. Its a nice paycheck regardless, and i don't complain.
So to summarize: don't quit your day job. Appraisal work should supplement your income and not be your only source. I don't know of many appraisers these days earning more than $100,000. I'm sure there are some, but i'm willing to bet the majority are lucky to clear $50,000.
You may want to consider becoming an agent while you're at it. Make money working the distressed sales side of the business, with appraisal work on the side.