It's a sin to tell a lie (or 'twas, anyway; it seems a bit less so nowadays, especially if followed up by a public apology of some sort), but poor spelling has never been more than a minor peccadillo. Someone advised me the other day that we're living in a "post-spelling age," which may very well be true; sadly, I think the same might be said of good manners. "Dear Sir," we used to sexistly, if politely, start off our business correspondence—which would then conclude with the de rigueur sign-off "Sincerely yours." It wouldn't have been a sin, surely, but certainly cause for chagrin, if we had written instead Sincerly. Even back in the "good old days," I think I must have been nostalgic for even better ones (or better yet, British ones) when I fell for Sidney Poitier and Lulu in the 1967 classic To Sir, with Love. I'm being completely sincere when I say that there were six examples of today's typo in OhioLINK, and 52 in WorldCat. Will you come up empty in your own catalog? It's possible, I guess, but in another "conflated idiom" (or something rather like that), which was sent to me recently by a friend: "I severely doubt it."
(Movie poster for To Sir, with Love, courtesy of Wikipedia.)