I have V brakes on mine, they work pretty well, but I'm not quite satisfied. I'm going to switch the front wheel V brake out for a disc brake, should give me a lot of extra stopping power, since most of the stopping power comes from the front wheel anyways. However I'm not sure how most V brakes work, I have a friend who runs a bike repair buisiness out of his garage and has a wholesale license for bike parts and gets stuff for me at parts cost, so I was able to put the motor on a $1500 cross bike (I paid him $600 for it) which I had completely customized for myself. So I have very good V brakes (they can lock the rear wheel at 30 mph if I pulled hard).
Now for a question of my own: My bike has a hybrid aluminum-carbon frame (aluminum on the outside to give spots to attach stuff and make it hold up to abuse, layers of woven carbon fiber on the inside to give it extreme strength while being lightweight), I have seen people saying that aluminum frames don't hold up, and that steel is the way to go. My question is, does anyone have any experience or speculation about how a hybrid aluminum-carbon frame will hold up with a 66cc motor attached, and how soon will I be able to tell if it's not holding up?