In a grab-bag post of Google searches that led to her blog, Lynn Sislo makes the statement that John Williams ripped off the main motif of his score to Jaws from Dvorak's New World Symphony.
Until I hear from the lips or pen of Mr. Williams himself that he did, in fact, "rip that motif off", I won't believe it. The motifs are the same in their notes only, and not even for that long; the rhythms diverge very quickly, as do the notes themselves, and the orchestrations and dynamics are totally different. Williams limits himself to just the double basses; he plays them slower, lengthening the pauses between statements of the "duuuuuhhh-dum" motif (because it's a suspense theme); and when he goes into his full rhythmic statement, it really doesn't bear much resemblance to the Dvorak at all when you actually listen to the way Williams goes on from there. Dvorak uses that motif to very quickly lead into a big brassy statement of the main theme of the movement, whereas Williams uses the motif to set a mood of menace that doesn't let up even when his main theme is sounded in the low brass. And Williams's use of the same motif is much more rhythmically pulsing than Dvorak's.
It's entirely possible that Williams, being a very experienced musician, decided to use the very bare-bones of the Dvorak motif -- and I'm talking just the first bar alone, those two notes, because after that it's totally different -- as a basis for a suspense score, but to accuse him of "ripping Dvorak off" suggests to me an accusation of laziness, a kind-of "Williams couldn't do it on his own, so he stole a bit of Dvorak to help him out" thing. If this is what is meant by saying "Williams ripped it off from Dvorak", then it makes little sense, since Williams uses that motif as the basis for one of his best filmscores, whereas Dvorak just uses it as a six-bar introduction to a movement in a symphony, and that motif is never heard again. The similarity between Dvorak's symphony and Williams's score is not very strong, and is over almost immediately.
And anyway, composers have been using and re-using the same motifs for centuries. Williams no more "ripped off" Dvorak than Shostakovich "ripped off" Richard Strauss's Death and Transfiguration in the final movement of his Symphony No. 5. The fact that a work sounds a tiny bit like a previous work does not mean that the composer of the latter work "ripped off" the former.