Gayle and nice on ice: If it was every exercise session, yes, I'd say 800 situps may not be the best way to spend your time. I do think that is something you'd have to determine, though. But, a couple of times may be something that challenges you. After all, the main thing I've learned from exercising, is that if I want to see changes then I have to do something different. Whether it is a change in duration, intensity, moves, more cardio, less cardio, higher rep workouts, lower rep workouts, etc. (I think you get the idea).
Sure, hanging leg raises are a tough exercise, but I don't think Cathe recommends them because you need special equipment for them. At the very least a bar you can hang from. I'm lucky because I have a large squat cage with a bar from which I can do pullups and leg raises. However, I had to get the arm slings because my upper body strength did not last long enough to get out enough reps to fully fatigue my abs. Also, you can cheat on these pretty easily if you swing your legs up. Then you use momentum to do the move. I don't think a captain's chair is harder even if it does make it harder to use momentum, because I've used the chair at gyms while on vacation and they always seemed a lot easier to do than hanging from my bar at home. Of course, that is just anecdotal evidence, so take it for what its worth.
Also, if someone can do 3 sets of 30 or 50, than I really take my hat off to you (as long as you're not cheating and swinging your legs;-) !) because it is a challenging exercise. I usually fall in the 10 to 15 rep range, though I work on it.
Finally, while hanging leg raises are a great exercise, they, like any other exercise are not the end all be all of ab exercises. Like I said before, it is a good idea to change up your routine. And though 800 reps seem like a lot, if you do Ab Ripper X from P90x you are doing over 300 reps. I've never counted the rep range in a Cathe ab routine because I like to concentrate on doing the move and not counting, so I can't say what they come in at, but I'd think they are pretty close since the times are similar. So, one go round of Ab Ripper X gets you pretty close to 1/2 way and actually you can add reps while Tony Horton is talking if you are familiar with the routine to make it 400. I also like to play with rep ranges. Sometimes I use my medicine ball with these routines to change it up. Usually the added weight means I can't do as many reps. Doing that sometimes can be a challenge.
Whew! That was lengthy! Anyway, best of luck with whatever way you choose to exercise. I love hearing about what other people do because I love exercise (I know, I'm weird!) and new ideas, etc. It keeps it fun!
