ESPN.com's Justin Ray says there is emperical evidence that the groove rule change has made a difference. Nice irony here as he has to crunch PGA Tour numbers because the USGA, like the other governing bodies, has not adopted the PGA Tour's outstanding ShotLink system to better document distance accuracy numbers.
Anyway, Ray writes:
On approach shots from the rough from 50-75 yards, PGA Tour players are hitting the ball an average of 7 inches further away from the hole in 2011 than in 2009, the last year players could use the old grooves. That's 2.6 percent further away from the hole.
On shots from 75-100 yards, that number is also 7 inches. From 100-125 yards, the difference increases to 9 inches, a 2.5 percent difference. When players are 125-150 yards away, the number is 15 inches -- a 3.6 percent difference.
That doesn't sound like much until you put it into this context: PGA Tour professionals make 56 percent of their putts from 7 feet. From 7 feet, 10 inches (so about the difference we see after shots from 100-125 yards), that percentage drops to 50 percent. A player can be anywhere from 1 percent to 6 percent less likely to make a putt (from any distance on the green) when it is nine additional inches from the hole.