"Peak air travel" by aircraft departures occurred in 2001, and by total passenger miles, I believe hit around 2007. There's some wiggling around that, in that load factors and seat pitches allow for aircraft to carry more passenger miles on average. But the US DOT's 2000 forecasts for aviation fuel were high by a factor of 50% or so for ~2013. (I've not checked the data since.)
"Peak car", by passenger miles driven seems to have hit much of the US also around the 2007-8 financial crisis. But if you look at underlying trends, as early as 1990 or thereabouts ownership and miles driven were softening markedly particularly in the Pacific Northwest.
"Peak Computer", in terms of traditional desktop (and laptop) sales is well behind us. Mid-to-late 2000s IIRC. Several factors at play, including market saturation, a stagnation in computer capabilities (CPU speed, RAM, disk, and a bunch of other factors have more-or-less been in a holding pattern, though energy usage has fallen markedly), and the increased convenience of the Internet in your pocket making mobile devices far more attractive. We may be seeing backlash to that (security, privacy, burnout, etc.). There remains the point that computing devices are fundamentally difficult for much of the population to use.
Social networks can grow quickly, but also crash with devastating speed. Understanding just what it is which makes them attractive ... and unattractive ... is a key point to understanding their strength. Or weakness.
