Since Nero asked this question under the Christianity thread, I'll attempt to give an answer. But it may not be the one you like if you are looking for a simple yes/no answer.
First, what is sin? We have to decide that first or this conversation is meaningless. Quite literally, in Greek, "to sin" means to miss the mark. It is like an archer shooting at a target. There is one bullseye and many "sins". In other words, God has a will for our lives. When we turn aside from that path we "sin."
So, is it God's will that we live miserably? I don't personally believe we serve that kind of a God. I will go out on a limb and say that there is indeed a lot of sin surrounding any suicide. I see sin in the people whose bigoted views have made life so hard for us, sin in a society which refuses to act justly, sin in the life of a person who wants to end his/her life just to make things easier without taking into account the destruction left behind. I see sin in institutions who have made others feel like the only way out is suicide. I could go on, but there is enough sin to go around here.
Now sometimes, however, the circumstances are different. Think of a soldier who makes a choice to fall on a grenade to save his buddies. That is suicide. Is it a sin? Hardly. What about those who hid Jews during WW2 and faced certain death rather than give them up. That was suicide. Is it sin? I don't think so.
And what about suicide in the case of severe mental illness? Is that a sin? The water gets quite muddy here.
I also think it is a sin to hold on to this life at all costs when the quality of life has gone, such as the elderly with terminal illness. Here the water is quite muddy as well. But I do know that Christians believe in life after life. One of the greatest ways to act upon our faith sometimes is to let this life go, either for us or for a loved one.
What about in hospitals when a treatment is sometimes worse than the disease? Is is suicide to refuse treatment even when it will bring death? I don't think so.
As far as "sitting on the brink," I assure you that I have been there, too. I haven't gone over primarily, not because I am worried about what might happen to me, but because I could not leave the ones I love with that mess to clean up. Having been on the other side of things, I assure you, it's tougher than most people think. It is out of accordance with my faith to do such an unloving thing.
Now I've said all of this without quoting Bible passages, but as far as the "hell" question, I simply point to one verse which is one of my greatest comforts in this life:
"There is therefore now no condemnation for those who are in Christ Jesus." Romans 8:1
Peace, all!

Kristi