I used to work in a David Lloyd club - they were the first chain of gyms to install them. Last year I was training for a marathon but had hamstrings problems - after using them every day for a week (they recommend only 3 times a week really, I think) I stretched out my hamstring and was able to run again.
I did a half marathon on Sunday, very stiff on Monday , jumped on one Monday afternoon - sat on it to massage hamstrings, and was able to run that evening without any soreness at all.
Great machines for stretching but that's about it really, in my opinion. Like you'e all saying, you've just got to do the work, not let a machine do it for you.