1) I'm not going to look it up because I'm afraid I'll find out it's an Urban Myth, but "Good artists copy. *Great* artists *steal*." -Pablo Picasso.
2) On a related note someone notable like Shakespeare once said something along the lines of that there were only 2 or 3 stories and everyone kept recycling them. For that matter, a lot of Shakespeare's plays were just retellings of older tales.
3) I've been on a nuBSG jag lately, and it's fun to spot the bits they stole from other stories. There are plots and concepts but maybe my favorite is when the criminal terrorist political prisoner Tom Zarak (played by the Apollo actor from the original series) becomes a...councilman?...and ticks off President Roslin. Earlier in the episode there was a question of whether she'd shake his hand (which was actually lifted from MidEast peace talks, IIRC) and she kisses him on the cheek. They meet again and she says "Don't worry, I won't kiss you" and he replies "Pity, because I shaved especially close with the anticipation of getting smacked by you." This is lifted almost word-for-word from the 1970s George C. Scott movie "Patton," where Patton meets Field Marshall Montgomery in Sicily.