I have an anterior placenta, and although they say it's harder to feel baby kicks, etc., I did not find this to be the case at all during this pregnancy. I felt LO kicking at 18 weeks, and his movements are very strong, and very much felt. In fact I had always thought my placenta was posterior until I read my midwife notes which told me different.
My friend just had an emergency c-section because she had placenta previa (placenta covering cervix). It was always low lying but they had hoped it would move. However it didn't so she was ordered on bed rest for the remainder of her pregnancy. They had her scheduled for a c-section at 36 weeks, but had bleeding just beforehand so they had to get baby out right away. Not an experience anyone wants, but baby and mom are fine.