I can definitely put my two cents here coming from my own personal experiences. When I was younger I used to be very confused about sets as well. I figured that "More sets mean more muscle growth", so I did anywhere from 35-45 sets for each muscle. Yes, 45 sets. I'd do 8-9 exercises for each muscle, 5 sets for each exercise. I don't want to provide examples of what my old routines looked like because it makes me feel like an idiot.
I think the reason I lived through it was because as hard as I was training, I wasn't training nearly hard enough. Thankfully, as I got older, I gradually reduced sets over the years when I realized I wasn't lose size or strength. 35-45 sets became 30-40 sets, 25-35 sets, etc...
Now I do only do 16 sets for the big muscles (Chest, Back, Shoulders, and Thighs) and 12 sets for the smaller ones (Biceps, Triceps, Forearms, Hamstrings, and Calves) and I have even better results then I did when I was doing those ridiculous routines. Hell, I'd like to do even less than that but if I do I honestly don't feel like I'm getting a "complete" workout.
As far as the split, I'll always suggest the old fashioned "push, pull, legs" routine which is Back, Bis and Forearms one day, Quads, Hams and Calves on another day, and Chest, Shoulders and Tris the other day. However if you find a different routine works for you, by all means do it. As far as abs go, I do them 3 days a week so I end up doing them on all 3 splits throughout the week.
Bottom line, from my own experience and from what I've read in dozens of books and magazines for the past 9 years, anything more than 20 sets for a muscle is overkill, and you should only do 20 sets for a muscle when you feel it's lagging behind.
Oh and any more than 25 reps on a set is overkill as well. 15-25 reps is enough to stimulate the
fast twitch muscle fibers. That took me a long time to learn as well.