http://en.wikipedia.org/wiki/Landauer's_principle
Supporting: http://www.stanford.edu/~rsasaki/AP202/YY3.pdf and https://encrypted.google.com/search?num=100&hl=en&lr=&as_qdr=all&q=2.85+trillionths+Watt+%2F++1+gigabits++41+exabyte&oq=2.85+trillionths+Watt+%2F++1+gigabits++41+exabyte&aq=f&aqi=h1&aql=&gs_l=serp.12..19.10626l10626l0l12026l1l1l0l0l0l0l159l159l0j1l1l0.frgbld.
Questions: How much consumes Facebook's delete operation and when will above become a problem?
(TIL 1 exabyte = 2^30 gigabytes, but I expect I'll forget again.)