I did this a little before new years. I was about 6 months into training and looked at it as a hazing experience before I could rightfully be allowed in the weight room.
I had been doing simple 5x5 and 3x10, so low reps, and trying to lose weight. I leaned out enough where I figured I should add some muscle.
My 1 rm squat at the start of the cycle was 305. I weighed about 170 lbs. I started the 20 reppers at 205/~68%. I did 2 workouts a week, and jumped 10 lbs per workout until I got to about ~75%. I did +5lbs per workout after that.
It started easy but eventually got hard. At about rep 15 I would let out a grunt/primal death scream, that would startle the whole weight room.
I ended the program 6-7 weeks later at a chubby 190 lbs. I got 18 reps at about 87% of my starting 1 rm. After that the progress fell off pretty quick and I called it a finished training cycle. My 1 rm went up about 10% and I was doing sets of 20 heavier than I ever squatted 5x5 w/.
I had skinny rock climbers legs before and now I have a bit of a squatter's butt.
The thing that really helped me when the weight got heavier was hitting some heavy singles before that set of 20.