Philip Jensen sent me the New Yorker quotation (from Nancy Franklin) by e-mail on 22 June 2007; a discussion then ensued on the American Dialect Society mailing list. A few days earlier, on 19 June, the Grammarphobia site coped with a complaint from a reader about this very expression: “One of my pet peeves is hearing people say “pawn off” when they mean “palm off.” Why do they say that?”
The most recent OED (December 2005 draft revision) has no usage note on the relevant subentry for “pawn”. It gives early cites (1763, 1787) for “pawn upon” — the first cite for “palm off (on/upon)” is from 1832 — and then cites (mostly from elevated sources) through 2003. MWDEU says the expression “would appear to have originated by similarity of sound to palm in palm off… but it may in fact be a dialectal variant.”
It turns out that OED1 and OED2 had an “Erron.” label on this usage, but that label has now been removed, presumably in recognition of the fact that, as we say here on the ecdb, the usage is “nearly mainstream”. Nevertheless, Paul Brians treats it as a straightforward error. (And Bryan Garner doesn’t mention it at all.)
Obviously, “pawn off” still rubs some people the wrong way, but there are others (like me) who don’t even notice it as worthy of comment.
[Thanks to Ben Zimmer and Jesse Sheidlower for supplying most of the information above.]