Having grown up abused by my own parents (in all ways except sexually), I identify with a lot of what he says. I used to think of suicide daily, now I just think of death. Counseling (sans drugs) is what helped me get there. It's good and bad now, but there's a positive trend.
I think what saddens me most about this note is his experience with counseling professionals (though he does use the word doctor, so "counselor" might not be totally accurate). My counselor's office is where I most feel like myself, it's where I feel safe. If only Bill had a situation like that, he might still be here today.
I didn't know the guy personally, but I've read stories like this before, and one thing that stands out to me is how amazing some people that have been through trauma like this are. He went through all the hell that he did, dealt with it on a daily basis, yet still had the capacity to do great work, to make people laugh, to attract others to him, and to generally do awesome things (http://blog.from.bz/2009/03/01/sudo-make-me-a-sandwich-stub-...).
Do yourself a favor and read the note all the way through. Pass it around. Remember that in general, half of the people you see every day have it shittier than you do. Try not to be a jerk.