From my personal anecdotal experience, I've seen firsthand some horror stories with altitude sickness. I will always tell people now to acclimatise, drink fluids, and follow the local tricks like chewing coca leaves in Bolivia. However, as far as I'm aware, the only "cure" for it is still to come down to a lower altitude (or pressure chamber).
For the most part, it doesn't matter how fit or healthy you are - it is seemingly random who it affects, and you can be fine one time and terrible the next.
I've been lucky myself to only ever get a little dizzy, out of breath and have headaches, and that's in several trips over 4000m.
What do you use to avoid altitude sickness, or have you seen methods which serve to delay the effects, avoid symptoms or generally get through it OK?