I am also aware of the influence it has had on Computer games, but it's also possible that these computer games would've developed independently of pen and paper RPGs. For millions of people play MMORGs as opposed to the pen and paper. But I don't know for certain, I am simply speculating.
Not likely. Look up Dungeons and Dreamers. It's a good book and goes to show how D&D was effectively essential in the development of the computer game. Also, Masters of Doom shows that without their D&D campaign, the original id guys would never have developed their particular brand of game that led to the most popular (aside from sports) sort of game ever, the FPS.
D&D is a form of entertainment and so it's impact is felt most powerfully in entertainment. Whether its regular mentions in 80s films and television -- good or bad -- or its effect on the look and feel of every fantasy film made since 1976, D&D has had a powerful impact on American entertainment.