Neil (mainly and others)
Now I am a techie (IT manager, programmer and gadget freak), and I didn't put any devices in my profile for about a year (of course I'm not on facebook either, walking a labrador seems to be a full time occupation

).
I agree with you that there are probably a large percentage of fly by advertisers.
But I suspect that most first posts don't have a device in their profile regardless of if they are trying to plug their book or not - who spends the time to fill out all the info if they are not going to post all the time.
Hey I just looked at my profile I'm averaging 0.08 posts per day chatterbox that I am.
Ah, well, back to lurking