As I responded in Email to Michael, I agreed with his surmise. But, to my amazement, I was able to find the issue in my basement. It was in the December 1986 issue. The article involved original research by Golf Digest, with equipment and technical expertise borrowed from Karsten Manufacturing. The conclusion was as Michael recollected.
Square grooves give some negligible spin increase from a dry fairway.
Square grooves give substantial spin increase from wet rough. They quoted Tom Kite that he didn't WANT to suck the ball back with any more spin that he could already give it. They pointed out that the high-handicapper almost always leaves shots short of the the flag when they hit the green. Dave This is an update of an article posted to the Internet by the author in June 1994.