Riviera's 480-yard par-4 12th featured the most penal rough during the 2006 Nissan Open, so it was the first hole I've looked at with the PGA Tour's incredible ShotLink system that is available to the media during tournament week.
Besides 3 inches of healthy rye, the 12th fairway was 25 yards wide. The combination of prevailing wind, rough and a narrow landing area made it play as the 3rd toughest hole, with a scoring average of 4.232. (The par-5 first played to a 4.299 average.)
However, a case could be made that the rough added very little in terms of defining skill or rewarding accuracy.
According to ShotLink, the scoring average from the fairway was 4.13. From the left rough, it was 4.28, and 4.26 from the right rough.
Looking at the scoring numbers provided in the screen capture to the left (click on image to enlarge), the rough on 12 did not seem to impact scoring much despite the obvious attempt to penalize those missing the fairway via narrowness and tall grass.
I've taken the left and right rough numbers and combined them to get these percentages:
7% of tee shots finishing in the rough made a birdie
9% of tee shots finishing in the fairway made a birdie
63% of tee shots finishing in the rough made a par
70% of tee shots finishing in the fairway made a par
30% of tee shots finishing in the rough made bogey or worse
21% of tee shots finishing in the fairway made bogey or worse
And according to ShotLink, here's the scoring average by distance off the tee:
320+yard drives averaged 4.04
300-320 drives averaged 4.15
280-300 drives averaged 4.19
260-280 drives averaged 4.33
240-260 drives averaged 4.57
<240 drives averaged 4.70
The "proximity to the hole" data from ShotLink would also seem to indicate that flogging is an intelligent strategy. (Click on image to enlarge.)