I won't claim to be an expert of any sort about whether or not to use the rear brake. But I do know from my years of dirt-bike riding growing up that the rear brake is very useful when you're trail riding.
Speaking of which, I just signed up for the MSF Dirt Bike course over in Alpharetta next weekend. Looking forward to what should be a fun day of riding. I have to do that one so that I can take my GS over there in March for an Adventure Bike Course.
![Grin ;D](http://forums.sohc4.net/Smileys/default/grin.gif)