Surely, the media, and everyone in general, must be more sensitive to the toll that "celebrity" is taking - the news recently has been filled with shocking tales of drug abuse and public misconduct, involving genuinely talented actors and singers, that many people love. Ledger was, by all accounts, including his own, sensitive to the glare of public interest and media comment; and obviously a highly gifted actor. Personal problems had recently impacted on his fragile nature, with the result that, apparently, he had trouble sleeping. All creative artists know that state. I don't have much more to say, now, about this sad sad news - except that this feels very large, indeed, like the death of a James Dean for our time.
Ledger's Brokeback Mountain performance was a star turn, and powerfully revelatory of great things ahead. His Joker role looks terrifying and very dark, indeed, from the stills I have seen. Ledger had many more films than Dean in his oeuvre, though perhaps less of an established screen persona. But no one expected this, now. And it has hit around the world, on the day of the Oscar nominations, as if nothing else had happened. Our thoughts must now go out to those who knew and loved him well, and hopefully the spotlight will no longer torment the brilliant young man. The BBC has some tributes here. David Thomson has a good post here.