1. be familiar with表示“(某人)对(某事)是精通的、熟悉的”, 句子的主语总是表示人的名词或人称代词,介词with后接表示事物的名词。如:
Most of us are familiar with the pop star.
John was very familiar with this kind of situation.
2. be familiar to“(某事)对(某人)是熟悉的”, 句子的主语总是事物,介词to后接表示人的名词或人称代词。如:
The pop star is familiar to most of us.
This kind of situation was all too familiar to John. (=very familiar)