Ah, this might be what Apple was talking about when it claimed it was the "number one portable game player".
While the comment made recently by Steve Jobs raised eyebrows - mostly because he never backed it up with figures - research from NewZoo shows that while Apple's iDevices (iPod Touch, iPhone, iPad) are the second-biggest games devices in the US, they're rapidly gaining on Nintendo in first place.
NewZoo reckon that 40.1 million Americans use their iDevice to play games on, compared to Nintendo's DS install base of 41 million. Now, this is a research firm extrapolating figures based on sample groups, not the US Census Bureau, so those numbers won't be water-tight. They are, however, indicative of a trend that will inevitably see Apple's devices overtake Nintendo's as what you'd probably call the "most-used portable gaming system".
That's not in terms of individual use. I'd never play an iPhone game for 200 hours like I did Advance Wars DS. But it is in terms of the number of devices out there that people are playing games on, and casual/rubbish games many of them any be, it's still impressive that Apple has become a challenger to Nintendo (who despite claims to the contrary are in direct competition with Apple for mainstream consumers' spare time) without ever actually releasing a dedicated gaming platform.