I've been around for almost four years and, as an instructor I find this forum invaluable and recommend it to every instructor I know.
A couple of aspects stand out:
This is a SAFE place. There is little or no intimidation that goes on here. No name calling, no bad mouthing. The result is that people feel good about posting videos and expressing their opinions on issues. So, when preparing for exams this is a great place to try speaking your mind. Sure, you may get people who disagree but they don't make you feel stupid because of it.
And, because it is safe people feel good about posting videos here. The opportunity to do movement analysis off a video and compare what you see to what others see is invaluable. Because everyone looks at things a bit differently you learn to pick up on things that you might not have if left to your own.
Second, the CONTENT here is phenomenal. I know when preparing for my Level III and my DCL exams I spent many hours reading and absorbing material. It greatly enhanced my professional knowledge (which is something you are graded on) and my teaching ability. I can remember one great Bob Barnes post that I borrowed from, modified to my own style and used in an exam. Not only did it score well as a teaching session but it made a great change in at least one person's skiing in the exam.
Lastly, building friends. I've only met a couple of people who regularly post here and all have been fun, really nice people. I think because of the first two aspects we tend to attract these kind of people as opposed to the, well, let's just say, not so nice people.
Those are my thoughts...