Yup I do.
Flexibility is about strenth, if your muscles, tendons, ligaments etc. are strong in stretched positions they will allow great flexibility.
A stetching machine is taking what is there, and if a person is in poor condition or just gets overzealous in their persuit of flexibility then a lot of damage can be done.
Please refer to www.stadion.com/column.html
for a professional's view on the matter.
PNF is good but it was really designed for illness - not sport.
Sport specific stretching is also discussed at www.stadion.com