I was going to ask this question cause it's bugged me for a while. You always hear about new bikes with their fancy radial mount brakes, but apparently I didn't get the memo explaining what they were. I thought I had googled it to no avail, I know I checked wikipedia, and I never got around to asking here. But just before I did ask, I did one more google search and found my answer. So now I'm posting for those that may be curious.
Basically, the brake caliper is mounted at both ends, not just the trailing end (closest to the fork). Also, the radial mount caliper is mounted at the back of the rotor, not just next to the fork and the bolts are parallel to the rotor. Illustration (from carbibles.com):
(http://www.carbibles.com/images/radialcalipers.jpg)
I don't have time (or complete understanding ;) ) yet to go into the reasons for why this is better. Maybe later or maybe someone else can throw their $0.02 in
Here's some background material:
http://www.motorcycledaily.com/13november02radialbrakes.html (http://www.motorcycledaily.com/13november02radialbrakes.html)
http://www.carbibles.com/brake_bible.html (http://www.carbibles.com/brake_bible.html) (about 1/3 to 1/2 way down the page)
http://news.motorcycle.com/article.motml?sid=1673 (http://news.motorcycle.com/article.motml?sid=1673)
The most significant advantage and main reason radial brakes came about is to reduce fork vibration caused under braking. If you look at a normal mounted disc caliper, the mounting bolts are perpendicular to the brake disc, meaning that if the disc moves slighly and flexes latrally this is picked up much more easily by the mounting bolts i believe. In radial mount callipers the mounting bolts are parallel to the brake disc meaning less vibration is picked up from lateral flex in the brake disc.
nice