I had it done to upper and lower lids. Unfortunately one eye did not heal as well as the other and although its fairly minor it left me with a slight pulling to the lower part of my right eye. The surgeon tried to correct this, but it really didnt make much difference. That was over a year ago now and I am still considering another operation to try to correct it. They still look better without the bags, but it took a lot of the pleasure away because they are not quite right.
So consider it all really carefully because theres no going back once its done and although I think I was rather unlucky it can happen!