For me, I am too young and have no desire to have children until I frivilously spend money on shit (like rhinoplasty and my hairline lowered) and get my career going.
This would actually, despite me not wanting to say so, be a deal breaker for me. But that is because I've spent so far all my youth in school and starting a career-- I want to have a few years where I can be SELFISH and focus on me. Have a child? That child should be your focus, and any fool saying otherwise is denying that child a proper upbringing. I've dealt with enough children coming from homes where parents went on trips to Hawaii and such and nonstop left the child alone, it is sad. Really sad actually. If you cannot commit to the child, then you cannot commit to the relationship. That is my opinion and I hold onto it stubbornly, I've had too much first hand experience with parents being selfish and neglected children.
ON THE OTHER HAND THOUGH, if you are ready to make that commitment and to love this child as if he/she was your own... go for it. I think there is a lot of beauty in that, and if you are ready for it I totally encourage and support you. But realize that this is, assuming you're not looking for a fling, going to be MANY YEARS of commitment. Sit down and think about your own life and what you want out of it, and be HONEST-- do not paint yourself as a saint. Honestly sit down and think if you're willing to spend of your own salary on this child, if you're ready to pick them up from school, if you're ready to bandage their wounds if they get hurt. Be ready, and be honest. If you are ready though, as I said earlier, totally go for it.