A useful article from Search Engine Land includes some useful stats which show how mobile and tablets are performing across certain sectors:

Another trend which was first identified by Adobe Research last year is that tablet devices bring a higher ROI than desktop. Whilst the reasons have not been identified, it is likely to be a combination of factors. Until very recently, the tablet landscape has been dominated by the iPad, which is largely bought by those in higher income brackets. Add to that the rich user experience, accessed from almost anywhere in the home, and you see a higher purchase value in retail. There is more here in this very useful report.

Mobile specialists are aware that different handsets and operating systems appeal to specific demographics. The chart below supports this, as it shows how Android and iOS deliver different ROIs: