Jim Wendler had an article recently called the 100-rep challenge.
100 reps seems like a killer workout, and probably a little excessive. Why 100 reps? Don't reps become pure endurance at this point?
The answer is, basically, no. By doing 100 total reps of a reasonably hard weight, you build both endurance and muscular size. It is a combination of a lot of reps (your strength-endurance) and a lot of time under tension, which is considered by some to be the most important component of muscular hypertrophy. It doesn't hurt that anything you could do for 20+ reps you probably should be able to do 100 times total . . . if you are mentally willing to keep doing the reps.
This isn't a new idea. I've been doing 100-rep sets for a while. I obliquely discussed it here (Rest-Pause Variation, but here is the "full" version as I have done it, taught to me by my MMA instructor.
Pick an exercise, preferably one with a low failure point (you won't be crushed under a bar from a squat, or round your back from a tired deadlift, or drop a weight on your head). This is a good place for exercises that are easy to ditch - cable rows, kettlebell snatches, bodyweight squats, pin barbell bench in a power rack, etc. You need something you can do correctly even under a high fatigue load.
The goal is to do 100 reps in one set. Pick a weight - something reasonably heavy for that exercise, but still quite light - I'd suggest around 40-50% of your one rep maximum, at most. Do as many reps as you can, then rest for one second for each rep you did. If you got 60, rest for up to one minute. Get 10 more? Rest 10 seconds. Keep going until you've gotten 100 reps.
Each time you do the workout, get the reps done in less sets. When you hit 100 reps in a row, up the weight (or add a second set).
This approach really does work for building strength-endurance, and it doesn't hurt your muscle size, either. It is excellent for training that requires a lot of strength-endurance, such as grappling, wrestling, or martial arts in general.