Disposable diapers contain tons of chemicals and dioxins that are toxic. Most disposables (even those "green" brands) contain chlorine. Urine is basicly ammonia and when chlorine and ammonia mix, they form a toxic gas - not enough to kill anyone, but enough to make most babies breakout is rashes.
Disposable diapers do not allow baby's skin to breathe. Cloth diapers are more comfortable, breathable and have super soft interiors.