Ok, Here's my take on it. Abs are mainly made up of "fast twitch fibers" (just like bi's, legs, chest, etc) I think you would be overtraining them if you doing them EOD. And sure pumping 50 reps might make them burn but it doesn't "mamximize" development of the muscles. You wouldn't go and pick up 10lb dumbells and curl 50 reps and expect to build better bi's would you? I train my abs like any other muscle group. Using both low and moderately high reps and overload the muscles so the abs develop. Ususally once a week. Like Presser said, thay also get worked during other exercises as well. (squats etc.) But no matter how great your training is, if you aren't lean, you won't see them. So proper diet and training I think are the key.