I've recently developed this problem too. It doesn't happen all the time for me. Seems to me that most of the ones that go right are because I'm trying to rip the ball into outer space. I find that if I let the club do the work and don't swing so hard my teeth clench I have a much better shot of hitting it straight. Also, a friend of mine told me my swing tempo was bad. I bought an IPod and listen to it while I practice, mostly classical music, and that seems to have helped a lot.