11B, in my experience the rear brake is very valuable in the rain as a traction feeler -- I'd rather lock up the rear than the front.
With my BMW, the front suspension is designed in such a way that that the bike will skitter and lock the front wheel before the rear will lift -- this isn't a complaint about the BMW, in fact it can stop as hard or harder than most sport bikes. But, because of the suspension and the weight distribution, using both brakes will provide better stopping power in pretty much any situation than using the rear alone.
Further argument: if a rider hits a patch of gravel, oil, or goes off road, being able to use the rear, and to modulate both brakes becomes invaluable.
In my experience, it's possible to ride on good clean pavement without the rear brake -- but if I always ride that way, I never develop the skill to use the rear brake -- I won't have that skill when I most need it.
Of course the rear brake is good for the rain, which is also mentioned in the link I provided - but then, riding in the rain and emergency and or track braking are
quite different circumstances (both of which I personally choose to use both brakes).
So, once again, as I already stated, I feel the rear brake causes more grief than it helps. To each their own. Safety first.
A few examples of the thousands with the rear brake having a detrimental impact on riding:
http://www.bayarearidersforum.com/forums/showthread.php?t=303488
Their was also a recent death of a forum rider who locked up his brakes, R.I.P..
Of course, each and every rider should continually strive to improve their skill but each one of us also needs to know our current limitations, and many, many, many times, the rear brake can become part of the problem instead of part of the solution. That means, for some people, they should stick to "practicing" the technique until they have gained enough skill to "implement" it when it counts.
For the most part, do you guys use only the front brake when riding?
Some people have noted that their are different types of circumstances encountered as you ride so I'll update my overall answer.
Normal conditions - 10 mph and under rear brake, everything else Front.
Rain - more reliance on rear brake - better to lose the rear end than front in the rain, plus I want the most available traction for the front tire as possible. The front tire only has so much available traction which is even more important in the rain. Obviously, the harder the front end brakes the less available traction we have, and when you combine that with a heavily loaded and turned over front tire - disastrous things can happen, especially in the rain.
Emergency stopping or the track - both brakes but even then, you're only on the rear brake for a very short period before the front end becomes fully loaded.