I've not watched Brokeback Mountain, but I've watched him in The Patriot, Monster Ball, and last, but not least, one of my favourite movies, A Knight's Tale. He's a pretty good actor, IMHO.
It's pretty sad reading about this, but it does shows how tragic it can be whenever drug abuse intertwines with life. Stay away from drugs, kids, else they will definitely have the last laugh.
Here's the link to the BBC news report: http://news.bbc.co.uk/2/hi/americas/7203797.stm