Yoga for skiers1. Balance is a learned skill that gets better with practice. There's some (a little) balance training in Yoga, which is helpful for skiers--as any balance training would be. IMHO, you get a lot better bang for your half hour doing other progressive balance training on other aids (foam roller, BOSU, balance disk, bongo board, physio ball, or even a pillow or crumpled towel) especially if you add a strength component or a weight shifting component, which more closely resemble skiing.
2. On flexibility, the advice I got after my MCL tear was different than what LisaMarie was told, but that was probably because I have a different body: I had the classic guy/former runner flexibility imbalance with very flexible ankles/calves but very tight hamstrings/lower back. They wanted me to get more flexible hamstrings. (Although, frankly, that was the only direction I could go...)
3. Yoga's benefits vs. risks really depend on your instructor and whether you have the sense not to follow him or her into insane places for your particular body. The gentle stretching to the point of tension/listen to your body folks=good; the must-twist-into-pretzel-one-traction-fits-all=bad. Getting the foam blocks/belts help there, to introduce yoga to those of us who don't have a background in ballet.
4. In terms of conditioning for skiing, yoga has some benefits, but is not as tailored as weight lifting, plyometrics, balance training, ski-oriented-circuit training and the various things you'd read in Skiing and Ski Magazine's fitness archives online. BUT yoga really is amazing, a total zen concentration on the body. When I did it, I found it really almost mind-altering, as the whole world (and the internal monologue) completely went away for an hour. (No thinking--geez, got to get the tax return done when I get home...) In that respect, I actually found yoga just like skiing: Totally absorbing, totally centering, and after an hour I had a BIG smile....