Recently I discussed with Jim Terman whether the possessive of "C.S. Lewis" should carry an extra "s" (Lewis' books or Lewis's books).  This led to the Wikipedia article on apostrophes, which we assume is authoritative because it is, after all, the Wikipedia, ahem, source of all knowledge.  

The article pointed in turn to the style guide "The King's English," by H.W. Fowler (1858-1933).  The Second Edition (1908), online here, proves that snarkiness is not a recent invention of the blogosphere.   Fowler says, for example, that omission of the conjunction "that" is "quite legitimate, but often unpleasant."

He also derides "Clumsy Patching" thus:
"When a writer detects a fault in what he has written or thought of writing, his best course is to recast the whole sentence. The next best is to leave it alone. The worst is to patch it in such a way that the reader has his attention drawn, works out the original version, and condemns his author for carelessness aggravated by too low an estimate of his own intelligence."

[This is exactly why I re-write my stories over and over, with pen, computer and typewriter, until I either get it right or concede defeat in creative exhaustion.]

Fun reading for those avoiding actual writing.

As for Mr. Lewis, I come down hard in favor of "Lewis' " rather than "Lewis's."  "Lewis' " would be parallel to the "Jesus' " construction which is preferred in Christian circles and which "Hart's Rules" (from the Oxford University Press) describes as an "accepted liturgical archaism."  Sometimes it's fun to be archaic.