My baby sleeps on her own crib starting day one and I was breastfeeding till 9 months. She is almost 10 month now and she sleeps on her crib during nap and night time. We trained her to fall asleep on her own at around 3 month and the first 2 days were a bit tough. She did cry but for only 15 minutes and fell asleep. Same for the second night. I remember nap time was easy to train at that time, but gradually she is ok now when we put her down at night time. The book I read suggests people start training at 4 month and I just follow what the book said.
Basically you need to have a routine, for example, in my case, bath time, dinner then sleep. Also, baby at this age should sleep at around 8 to 9pm. If they sleep too late, they will wake up more often because they have a hard time falling asleep by themselves. This is the book I read http://www.amazon.com/Healthy-Sl ... Child/dp/0449004023 and it really helps!
Many of my friends' baby started sleeping with them when they were sick, but as other moms said, after they recover, they don't want their own crib. Hope this helps