ubicomp

an interesting list, which i might let speak for itself:

pda, ipods shipped: approx 85 milion each
game console ownership: 200 million
pc usage: 850 million
internet usage: 1.1 billion
landlines in use: 1.3 billion
tv ownership: 1.5 billion
mobile phones usage: 2.7 billion

source

these numbers are all approximations, obviously, and not all directly comparable (shipped pda's can't really be compared to mobiles in use), but for comparison purposes, it serves a useful function. the direction of ubiquitous computing research would appear obvious to me...