I've been doing a weekly yoga class at Chicago Yoga since the beginning of the year. After coming in with the standard-substandard level of flexibility that comes from a regular running program (tight hamstrings, leading to tight back) and growing up playing lots of tennis (asymmetrical back, shoulder, and arm development), it took a long time to get to a place of reasonable flexibility. Even now, God help me if I show up for class after a night of drinking, or with low potassium or hydration.
With practice, though, I'm occasionally progressing to the more advanced forms of some of the poses. Once, I managed to do Crow Pose, which if improperly done results in an impromptu somersault. This weekend, I pulled off a really nice Extended Side Bend with backward noosed arms. I'd never been able to get my arms around my leg and back far enough before, so something in my shoulders seems to have loosened up nicely.