If you want to build your abs, then you need to increase the weight you move rather than go for frequent high reps.....like Spatts said. However, if you just want to 'see' your abs, then you need to diet the fat off of them rather than do frequent high reps. You get the message that frequent high rep ab work is not the solution either way? I also like cable crunches (I do them seated rather than standing), or lying weighted crunches, or whatever. The important thing is to work them heavy and then let them rest, just like any other muscle. And form IS everything when it comes to ab work. There's little point in just going through the motions and counting to 60. Make every rep count 110% in both directions. If you do it right, you don't need many reps and you can't DO many reps.