I believe that anybody who lives has a life worth living. It's more of a matter of preference really. If you experience nothing but bad things in life, you will probably never see the good and--in plenty of cases--contemplate suicide. (Not sayin' you are on that level)
My brother for example. He told me (well, and you too Chaos) that he was contemplating suicide due to his current position in life; what with being homeless and having lost his mother just this past autumn. He may feel like life is no longer worth living and therefore, decides to think of ways to rub himself from exsitence. Though he hasn't attempted anything, sometimes I feel like--and I hate to say it--he might as well, because he's just trudging through life with little to no thought about his actions, or the consequences that would follow. So maybe he feels like that...
I really can't speak for others though. I feel like my life is worth living every day. Even in my rough times, I feel like I have to continue living until it is my time to go. I have too much ambition to just give up on life and I have too many goals, not only for myself but for my son and my younger siblings who don't really know how the world works yet. On that note: My son is truly what keeps me tethered to reality and keeps me in good spirits. He's my main reason for living and if he can enjoy life, then I can as well.
Life is very under-appreciated by many and there are few who realize that it's the most precious gift you could ever recieve.