My 4 year old wrote his name backwards in preschool. The teacher told me that she considered him to be very smart because it is not easy to do it. I have since seen him write with both hands as well as write mirror images of words and sentences backwards. He still has letter reversals at 6 years old, so I thought this ability was what was making him reverse letters while writing normally.
And my DS can read a book by holding it upside down. Nobody believes this if I tell them (including the pediatrician!).