In reply to Rob Exile Ward:
I've only been in September, about 12 years ago, but a French guide I got chatting to in the Pyrenees was of the opinion that June was the best month to visit Corsica as the temperatures weren't too high, there were less thunderstorms, there was enough snow for scenic purposes but not enough to cause problems and the valleys were full of flowers.
I've done some of the Mare et Mare Nord and it was really stunning. The huts are good, Pascal at A Sega is a real character, assuming he is still there with his horses, his semi feral hunting dogs and his vast collection of firearms.