They teach you to stretch the leg this way in Bikram yoga also. You really feel you're getting that "super stretch" (Bikram's words) on the hamstrings. You're really just screwing up your knees.

Here's a question: Will hypermobility (and the possibility of permanent, irreversible joint damage) help you drop some drunk in a bar on his ass faster? Let me know. I'm on my way to a bar.