I find the V-brakes need adjustment every 1000 miles or so. The cable travel is greater on these brakes, so a small amount of pad wear can warrant adjustment. If you ride in the rain or you are timid on mountain descents, you may even need new pads after a few thousand miles. I find brake wear somewhat unpredictable. At times, I've worn out brake pads in as little as 2000 miles. At other times, I've gone 6000 miles on the same pads.