Today Nick pointed me to this article by Ian Bogost that asks a similar question with regard to game design, with particular focus on casual games. Ian maps out the casual game space in terms of the player's level of involvement:
Applied to games, casual as informality characterizes the notions of pick-up play common in casual games while still calling for repetition and mastery. This is why casual games can value both short session duration and high replayability or addictiveness. Casual games may allow short session play time, but they demand high total playtime, and therefore high total time commitment on the part of the player. Low commitment represents the primary unexplored design space in the casual games market.
[...] If Casual Friday is the metaphor that drives casual games as we know them now, then Casual Sex might offer a metaphor to summarize the field’s unexplored territory. If casual games (as in Friday) focus on simplicity and short individual play sessions that contribute to long-term mastery and repetition, then casual games (as in sex) focus on simplicity and short play that might not ever be repeated—or even remembered.
While I'm not sure how well these conceptions of casual games literally map back to the world of information visualization (although the "Casual Friday" model sounds like the sort of happy relationship with visualization tools that I could support), the terms of the analysis undoubtedly do. Just as casual games took gaming mainstream, a "pick up and play" paradigm will have to define popular encounters with information visualization tools. And while the "easy to learn, difficult to master" casual game design philosophy already echoes Ben Schneiderman's long-standing information visualization mantra of "Overview, zoom & filter, details-on-demand," there's certainly more insight to be gleaned from the sort of contextual consideration Ian presents here.