Those shakeweight commercials are hilarious... I'm pretty sure the weights themselves are actually somewhat dangerous to use, but some of the exercises shown in the commercial just need some bass slap to complete the softcore porn theme...
I haven't used a bow flex, but I have used other all in one type machines of similar quality and the biggest drawback I see to something like a bowflex is the cost, for the same money you could buy a set of weights, a spotting cage, bench, bars, etc, and have some change left over. Some exercises won't be possible/reasonable on something like a bowflex, deadlifts for example, probably can't be done effectively (if at all). Squats on machines are usually enforcing some degree of bad form if you aren't the right height/etc for the machine (if it's possible to do squats on it) etc. A HUGE plus to the all in one machines though, is they are extremely easy to use. You pull a pin and put it somewhere else, or squeeze a handle and move a bar or whatever, the point is you can usually change weight and exercise with a very minimal effort. With a freeweight setup changing bar height means unloading the weight off the bar and then loading it again, just pulling the clips off the bar is more work than it takes to change up your exercise and weight on a machine, that tedium/time consumption has a pretty negative impact on my workouts, though I currently lack dumbells which would provide a quick swap out exercise between sets of heavier compound exercises. Those machines while large, are generally a LOT smaller than a comparable freeweight setup.
Some machines involve using a bar on a pulley with a cable attached to weights, these machines always give me a 'polish armwrestling' phobia, on the off check that a cable snapped or something.