Using a play yard instead of a crib?

Me and my husband are thinking about buying a play yard for our baby to sleep in when she gets here. We are curious to know though if it is really safe to use as an overnight sleeper? We would use the binet part and then switch to the bottom part and use those "quilted fitted playpen sheets"...So, are play yards really safe for babies to sleep in throughout the night? Does your baby or is your baby going to sleep in one and they are fine? Pls share any experience with these..thanks =o)