I've been browsing the forums (great place) and the other day I saw a post where someone used Google Earth to measure something. Thinking that would be cool, I installed it to check the distance of my longest drive to date. With approximate placement of the tee area, and pretty exact placement of the landing area (where it came to rest), my longest drive measured out to 298yds. My guesstimation is that roll accounted for only a small portion, maybe 10-yards of that distance as the hole is slightly uphill/sidehill, and the shot was hit after several days of rain making the fairways softer.
Having read many of the how for is your average drive threads, let me add a disclaimer... This is most definitely NOT my average drive, just that one that I truly hit pure and flush. My average good drive is in the 250 neighborhood. The actual average is greatly diminished when OB shots and major slices are taken into account.