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I always like to use the rear brake first which will load up the front end so when you use the front brake you wont get dive like you will if you only use your front brake.
I heard something a baja racer said on TV, he said never to use the front brake in loose dirt. I got to lay my bike down going down my mom's driveway and locking the front brake is almost a sure way to go down. At least if you lock the rears you will have the option of riding it out.
Is it possible you didn't catch the whole statement from the Baja guy? I've used the front brake countless times in loose dirt and sand riding offroad. Use of the front brake is a necessary skill to be able to get even close to competitive race speeds. It works best in a straight line but can be used in corners as well.
The front brake will bite the rider in a corner only if the operator isn't using his/her brain, the operator has to read the surface such as watching for dust, pea gravel, sand etc on hard surfaces, that stuff is slippery. 'Line selection' means avoiding those things which might give less than ideal traction, either accelerating or braking. Modulation is key as well, if going into a corner on ideal surfaces do not grab a big handful.
On asphalt, locking the rear and bringing it around on is a shortcut to the infamous highside; as the bike slows the rear tire will eventually quit sliding and when it grabs traction, oops over you go. Ouch.
Jensenman wrote: The front brake will bite the rider in a corner only if the operator isn't using his/her brain, the operator has to read the surface such as watching for dust, pea gravel, sand etc on hard surfaces, that stuff is slippery.
Hey! I resemble that remark!
Resembled it a few times over the years myself. 
The most memorable: I read a 'how to ride' article written by Scott Summers where he described using the front brake while entering a turn to help transfer weight to the front wheel to aid with turning traction. Man it had me all fired up. So the next time I went riding I started trying to use that technique.
I then discovered he's a much better rider than I ever thought about being. 
