A fellow yoga teacher and a good friend of mine has just completed her first Vipassana meditation retreats with her partner. You can check out her personal reflections over at her blog. Although I've never experienced this myself, I can see how Vipassana can be one of the most powerful and life-transforming experiences a person can ever have. Doing physical yoga asanas is just the tip of the iceberg of the whole experience of transformation. You are there, by yourself, for a total of 10 days--not speaking, barely moving, and meditating for the entire day. All the emotions you've managed to suppress throughout your entire lifetime inevitably rises to the surface, and the only way you can deal with them is to sit with them, face them, and ultimately let them go.
I remember during my teacher training we watched a documentary of people who had completed Vipassana meditations, including prisoners and criminals. They went in and came out as completely renewed people. They felt genuine repentance to the people and family they had harmed, and they vowed to become better human beings.
Vipassana is definitely on my bucket list. I don't think one can ever be "ready" for an intense 10-day meditation. It requires tremendous courage and belief, which I believe exist in every one of us.