Originally Posted by bostontrevor
If your wheel is spinning backwards that means it's skidding. You'll stop no quicker than if you simply had a rear brake. In fact, a brake that doesn't cause you to skid will stop you faster yet.
exactly.. as somone said before, the greatest stopping force is the point *just* before lockup.
Think about it this way:
Get in a car, drive in reverse at about 15mph, shift into 1st and jam on the gas. (this is a thought experiment, don't come whining when you make your clutch smell like burning

)
result: lots of noise, some smoke - sure sounds like it's doing something. BUT, it's going to take you a few seconds to go from traveling in reverse to forwards (and therefore passing the 0mph point)
Now, do the same thing, but simply jam on the brakes. You'll stop so fast you won't be able to keep your head upright. Jarring, huh?
Not only that, but it's a lot easier to manuver when none of your wheels are locked up -- whether you're in a car or on a bike.
Just my $.02.
Now, having said this skidding sure is a lot of fun (again: car OR bike)!