My Marin Muirwoods 29er came with Hayes MX4 cable operated disc brake which has been the least satisfactory component on the bike. The brake has one static pad and one actuated by the brake lever. The rotor deflects when the brakes are actuated.
My main annoyance is that the rotor is so close to the static pad that I'm adjusting it maybe once or twice a week with 5mm Allen key where I have to give it maybe 1/16 or 1/8 turn. It moves pad maybe less than 1mm. Any more than that and the rotor will brush against the friction material. The caliper itself has no adjustment other than the adjust for the cable and the knob for the inner static pad which moves it in and out only. Even with as little as a 300 ft descent I've found my self having to adjust the brakes at the bottom because my back brakes become more effective than the front which is pretty scary. And no it's not due to heating because the front brake won't work well again until after I adjust it even if I ride around slowly and let it cool for the next 20 minutes.
My riding is 100% urban so I'm stopping or slowing probably at least every 500 ft for intersections. And living in San Francisco, hills are a part of life. Climbing and descending 300-400 vertical feet with 8-15% grades is just another commute, grocery, or errand ride.
I've been debating on go with either Avid BB7 or Shimano Deore brakes. For Avid BB7, I can still use my existing levers and they're only $100ish for front and rear with new rotors. New levers looks like only $25 or so anyway for Speed Dial 7... For the Shimano Deore hydraulics, it will be $180 or so for pre-bled set of front and rear brakes but without new rotors.
Any reason to pick one over the other? And yes I realize that the Shimano Deore brakes is more than 1/3 the cost of my bike. Or maybe I should just upgrade the front brake...
I guess the bright side is that the friction material on my Muirwoods has lasted some 10 months but needs replacement soon. My coworker has completely worn out the V-brakes on his 7.4FX and has only had it since October.