I've finally found some demographic data for iphone and ipod touch users. The data come from a survey done by Admob and comScore, as published on the AdMob blog and reviewed by BusinessWire (which has figures not included in the blog post). The survey was in the first half of 2009 (presumably in the US, though this is not stated). I was after age data, which gives me this chart:
iPod touch ownership was highest among the 13-17 years age group (46%) falling sharply after age 25 (23% of ipod touch users were 18-24, 12% were 25-34 and 12% 35-49. After that it's single figures). iPhone owners are older - only 6% were 13-17; 20% were 18-24; 27% were 25-34; 31% were 35-49. This is pretty much what one would expect: iPod touches are cheaper and can be bought for a one-off payment (no ongoing mobile phone bill). So they are a possible (generous) Christmas or birthday present. In the UK at least, you still have to sign up for some hefty costs to own an iphone. So probably another case of "you can tell the men from the boys by the cost of their toys" as a friend of mine used to say. Speaking of men and boys, >70% of the owners (of both iphone and ipod touch) were male.
For other data (income, how mobile usage compares with usage of other media) check out the original article at AdMob
These data may go some way to explaining an interesting observation from "Just Another iPhone Blog" - "Do Crap Apps have legs?" The author comments on the curious popularity of "Crap Apps" - (applications that are trivial and/or puerile).