The success of games like Bejewelled, Diner Dash, Mafia Wars and Farmville is fantastic; more power to their creators. The fact that we're no longer enslaved to a single, constrained, and corporate-dominated distribution channel is most excellent. The opportunities for innovation - and profit - are enormous.
But "casual" has nothing to do with it.
Let me suggest an alternative way of viewing what "casual" means. We know that only 0.5 percent percent to 2 percent percent of people who download a casual game convert to becoming a paying customer. We also know that only a 1-3 percent of the people who play social network games ever actually pay money for virtual goods or game money, or sign up for one of the skanky "offers" that are an alternative to paying cash.
In other words, 90+ percent of the people who play these games will play them for free, but only a tiny proportion is willing to pay to improve their experience. This is true not just of games that have freeplay versions, like casual downloadables and social network games; how many people get exposed to advertising for a typical retail game, and what percent of them actually buy it? I'll bet the percentage is similar.
I submit that the best characterization of those willing to pay is "hardcore." That is, no matter how light or intense a game is, only a small proportion of those exposed to it in some fashion will be so gripped by the game, so in love with what it offers, that they are willing actually to pay. They are, by the terms of whatever genre into which the game slots, hardcore. Those who are willing to pay nothing are the casual gamers - they'll kill some time with the game, but they sure won't plunk down hard-earned cash.
What's happened in the last few years isn't a "casual games revolution" - rather, it's the creation of a new hardcore audience accessible via new distribution channels. And if your goal is to make money with a game, it should be to figure out what the hardest core of the genre in which you work like to play and are willing to pay for.
The hardcore is where the money is; the hardcore is the future. You're just dealing with a different hardcore audience now.
Greg Costikyan has designed more than 30 commercially published games in virtually every form, from tabletop to social network with computer, online, and mobile games in between.