'Eh, never really had too much of a problem personally, but my Xbox did delete all of my data on Halo3. And it still does it. Everytime I complete an amount of levels and unlock an armour, I'll go back the next day, and it will say that I haven't completed the missions before, and I don't have the armour.
I've also had an xbox break down on me, in the fact that the Drive wouldn't read any discs at all. First I thought it was my discs (Seeing as how a fair ammount of my discs break from poor care :P) but then, my perfectly new, never before used discs stopped playing, and wouldn't be read. Got an Arcade in the next few weeks, and popped my Hard Drive on it. No problems since.