I'm a Grand Master (waiting for points to hit to be GM2). I started judging back in 2007 so that I could understand what the judges are looking for when judging my beers. I could brew drinkable stuff, but after entering what I thought were some really good beers into competitions, I'd end up in the low to mid 30's. I figured I'd never brew better unless I knew what they were perceiving that I wasn't. It definitely helped develop my palate and introduced me to all of the styles, as well as practical experience with controlled off flavor tasting, all of which in turn drastically improved my brewing, since I no longer had to rely on the opinion of others to troubleshoot my own beers.
I agree with Amanda that the online materials are dated, and am glad that she has taken the initiative on renovating the learning materials. We've been eyeing them as needing work but have been working on other priorities (particularly getting more graders so that we can address the backlog problems).
Feel free to PM me or email me (steve dot antoch at yahoo dot com) if you have any questions about the BJCP or judging. If I can't directly answer them, I'll see that it gets to the appropriate person.