Out of my sample size of 1, I didn't take either of my devices -- my work phone or my personal phone -- to defcon or Vegas when I went last year: they didn't even leave my home.

I bought a laptop at Staples, put Fedora on it, used it for the conference, and I only really use it for when I go to conferences and the like.

There is a mix of folks using late model phones and burner phones, but, there there is a lot of burner usage at DefCon/DerbyCon/BlackHat.