[JoshTriplett]

> I am sure tons of applications that use gettimeofday() to keep track of time can break in subtle ways when seeing 59 twice.

gettimeofday doesn't return hour/minute/second divisions; it just returns seconds/microseconds since the epoch. Functions like strftime and gmtime handle the components of time. And leap seconds don't make applications see 59 twice; they make them see 60 once (58, 59, 60, 0, 1, ...).

Quoting the manpages for gmtime and strftime:

> tm_sec The number of seconds after the minute, normally in the range 0 to 59, but can be up to 60 to allow for leap seconds.

> %S The second as a decimal number (range 00 to 60). (The range is up to 60 to allow for occasional leap seconds.) (Calculated from tm_sec.)