With my first daughter, I could not bear the thought of putting her tiny little self into this seemingly huge crib, and then walking away...so she slept with us. She slept with us until about 16 mo. old, and then it was still hard to break her of the habit...every time she woke up, she would come in. She didn't start sleeping through the night "regularly" until she was almost four.
With child number two, I didn't want to do that all over again...but if you are nursing and want to get any sleep, you really have to cosleep for awhile. She is now almost 9 months old, and we started putting her in her own bed at around 6 months old.
For about a week, I would just lay in bed and look over at her and want to cry, but I knew it was for our collective good.
And you know what? Now I just love to wake up to her smiling face, jumping up and down in the crib, crowing and yelling "maa maa" every morning. It's better than waking up with your shoulders feeling like a ton of bricks because you've slept all gimpy to make sure you aren't encroaching on your baby's space in your bed.
BTW, my daughter (the youngest one) has been a tummy sleeper from DAY ONE (she just never, never would sleep on her back and because she was so strong, her doctor okayed it) and honestly, I felt safer about it after I moved her into her own sleeping area. In our bed, of course, there are sheets, blankets, a comforter, pillows, etc...in hers, just a mattress, fitted sheet, and tiny blanket over her. It seemed safer.