Are yoga and t'ai chi good exercises for someone with parkinson's disease? right now i am doing just fine with the meds, but i worry about later.

Yes.: Improve coordination and balance to prevent certain problems from worsening.

Yes.: There was a time when I discounted the importance of physical fitness in Parkinson's disease, because after all it's a brain disease and progresses without regard to conditioning status; but more recent studies have shown the benefit of any regimen of physical fitness or conditioning for those with PD. So now I encourage PD pts to stay fit in any way that works for them.