Chuck Berry and the Beach Boys

Listening to the "Surfin USA", it is clear that the Beach Boys "stole" Chuck Berry's song. This can be chalked up to no copyright laws, but where is the line between inspiration from another artist's work and directly copying it? A recent example is the controversy over Lady Gaga's new song "Born this Way" sounding very similar to Madonna's "Express Yourself". There are similarities between the two songs, but is it enough to say Lady Gaga "stole" Madonna's song?