Earlier today Oyster posted a new infographic in their blog which shows the reading habits of Android vs iOS users of Oyster's subscription ebook service. As you can see, Android users tend to read more during the day while iOS users tend to read at night (this might be biased by Oyster iOS app launching months before the Android app).
Android users were more likely to pick up a copy of Vonnegut, while iOS users read Philip K Dick. Android users also tended to read faster than iOS users, and spend longer stretches reading.
The following infographic is based on an unknown sample size, so it shouldn't be taken as a representative sample of all mobile readers, but it's interesting nonetheless. Feel free to make your leave observations in the comments.