Baaaaack in the day when I started karate, I would stretch like CRAZY for a half an hour before class. I never really got much more flexible. Then someone told me to stretch out a little before, and spend my extra half-hour stretching AFTER class. It worked like a charm. side-splits, front-splits, and I had a friend who was a little over 7' tall - and I could kick him in the face.
Now, after too many years of sitting on my can, I can't even do front-splits, and can barely set my foot on a 5'6 cubicle wall to stretch.