I haven't paid a whole lot of attention to Chromebooks; they're just too limited for what I'd want to do (plus, they probably send a lot of user data (think browsing history, in particular) back to Google, and I wouldn't go along with that). But they are kind of interesting, and this update on their sales is kind of intriguing, on a couple of levels.
The first is that they're growing. The second is that sub-$300 is a notebook market segment; I wouldn't have been surprised had that been too low to be considered its own segment for desktops, let alone notebooks. I wonder how sales of the iPad mini compare to notebooks in that price range.
The last reason that it's interesting is that Apple's profit on a Mac (all segments, not just notebooks) averages out at about $250, which is close to the total price on these notebooks. Strong evidence right there that Apple will never directly compete there (though my guess is that the iPad mini outsells by a significant margin every unit in that market segment, combined, and at a higher profit margin).