Plagiarism Or Subconscious Imitation?

From Sunday's Harvard Crimson:
A recently-published novel by Harvard undergraduate Kaavya Viswanathan ’08, How Opal Mehta Got Kissed, Got Wild, and Got a Life, contains several passages that are strikingly similar to two books by Megan F. McCafferty—the 2001 novel Sloppy Firsts and the 2003 novel Second Helpings.
The article provides a comparison of passages that appear to have been plagiarized by Viswanathan from McCafferty's books. Although the Crimson's case is compelling, I found myself wondering how to avoid unplanned repetition of another author's work, especially if you read favorite books many, many times. In The Not-So-Star-Spangled Life of Sunita Sen, for example, I named a character Elizabeth Grayson, and it wasn't until I reached for L.M. Montgomery's Anne of Windy Poplars recently that I realized I'd accidentally pilfered the name from one of my favorite authors. Also, some of the imitation in Viswanathan's book may be due to the generic "YASpeak" used by popular authors of teen chick lit. Well, we'll see how this particular publishing drama plays out ...