When my oldest (now 10 1/2 years old) was starting to walk, she also walked on her tippy toes, and I was told it was a "developmental delay." Well, she STILL walks on her tippy toes about 95% of the time. It's just what she does. She has NO (zero, zip, zilch) developmental delays. In fact, she has been enrolled in a gifted program for the last 3 years, and her teacher told her that the gifted program was actually too easy for her.
She is also VERY physically adept. She had earned her brown belt in karate by the time she was only 9 years old, and is very near to her black belt. She runs, plays softball and soccer, swims, roller blades, skis, snowboards, AND walks on her tippy toes.
I would say, that most children out grow it. The few who don't--well, as long as it doesn't effect them physically, don't worry about it too much.