I think I have. I actually analyze people's workouts when I go to the gym and give a thumbs up and thumbs down approval rating. Mostly, it's a thumbs down rating since what I see people doing doesn't (in my opinion) do much for their fitness. People spend way too much time on cardio machines doing long, even paced workouts. I don't know about you, but that would bore me senseless. I need to vary my pace and rhythm and get done quickly. I don't have an hour free to burn on an elliptical machine, or God forbid, a treadmill. I'd rather do rope or run sprints for 15 minutes and be done. Fifteen minutes of high intensity interval training (HIIT) will beat an hour of slow, even-paced cardio every time.
Today, I just came across an ad for the "Ab Rocket Abdominal Trainer." Devices like these don't rank high on my list of worthwhile purchases. It's a marketing gimmick, and I think it's more than likely total crap. I guess I can see how it'll give some people an ab workout, but if you honestly expect to get strong abs from this thing, you're delusional. People put far too much effort into training their rectus abdominus (the muscles that you see in six-pack abs). Ironically, those muscles aren't really the most important ab muscles for core strength. The obliques (internal, external, and transverse) are probably more important for core stability and strength. Overemphasizing the rectus abdominus serves no purpose other than causing "poochy belly" because the other abs aren't proportionally strong enough to hold the over-developed rectus abdominus flat. To add insult to injury, working the rectus abdominus more with tons of crunches won't actually give you a six pack unless you drop your body fat with smart exercising and a healthy diet.
Anyhow, I digress. If you really want to develop strong abs, do exercises that challenge your entire core. Stabilizing yourself on the rings, throwing and catching a medicine ball, yoga, pilates, etc. all develop your core. Heck, you can drop the ab exercises all together and just do proper full range of motion squats. You'll develop strong abs with weighted squats a lot faster that you will with overpriced, gimmicky devices that you see on infomercials. And you'll get toned legs at the same time. The more I think about it, the more squats sound like a cheaper and more efficient exercise than ab-rocketing the money from my wallet to the black hole of questionable exercise gadgets.