One way computers could aid pen-and-paper games, like D&D, without getting in the way is to provide visual keepsakes of mostly imagined adventures.
The players use computer models only as visual aids. Gameplay takes place entirely on paper and in the players' heads, but a program allows the players to create visual representations of their characters and gear. Like The Sims games and Spore, players could share art assets with thousands of others, so they could represent their characters with precision.
Then, after the players' PnP session is done, the program could be used to create pictures of the adventure's greatest moments. The setting could be layed out in fine detail, with the aid of props and beasts downloaded from the community collection. Character bodies could be adjusted to any positions. Facial expressions could be set by clicking on icons, then tweaked with the mouse.
In other words, let PnP gamers enjoy the complete freedom that makes the medium so much fun, but enable them to create "screenshots" of those adventures. There are already plenty of modeling programs. What I'm talking about is a modeling program that's designed for non-artists -- easy use, easy asset sharing, with a robust site similar to this.
Business-wise, I'd make the program useful for all PnP games, rather than make it exclusive to a particular one. What do you think?