I'd not known of this Ian McEwan "plagiarism" business before seeing this New York Times article linked from Locus Online.

"“If it is sufficient to point to a simultaneity of events to prove plagiarism, then we are all plagiarists, and Shakespeare is in big trouble from Petrarch, and Tolstoy stole the material for ‘War and Peace,’ ” wrote the Australian writer Thomas Keneally, the author of “Schindler’s List.” “Fiction depends on a certain value-added quality created on top of the raw material, and that McEwan has added value beyond the original will, I believe, be richly demonstrated.” If not, Mr. Keneally added, “God help us all.”"

Check out the scan of Thomas Pynchon's (typewritten) letter in response to the whole sorry business.

I can't imagine that these "charges" of plagiarism will have very much sticking power, but as the authors who have written in support of McEwan have suggested, if by some stretch of the imagination these sorts of similarities were considered plagiarism, I can't imagine that any work of fiction based on anything but the personal experiences of the author (or perhaps wholly invented secondary worlds, though maybe not even then) would escape the charge.