I run nothing but NimH in my planes. I love the light weight, and I am getting more flights out of an equivilent pack with the NimH over the Nicds. The only thing that I have heard, though haven't experienced it is, I hear that the NimH is drain to a certain point and then just dump their charge. I run the 4.8V 700maH packs in my 40-size Fun-Flys since I'm running high speed servos (otherwise i'd run the 6V packs with std. servos), and I normally re-charge the battery when it gets down to 4.8V, just in case.
Remember that you can't charge the Nimh with the same equipment. I bought a GP Triton and love it. I won't go back to the Nicds unless I need a little extra weight - NAH!
Kevin