Interesting tid bits i found whilst investigating the above message in a kernel log.

• The first leap second was introduced in June 30, 1972 at 23:59:60.
• The decision to introduce a leap second and the announcement is officially made by the International Earth Rotation and Reference Systems Service body.
• The announcement by the IERS for the 31/12/2008 23:59:60 UTC leap second can be found here.
• A questionnaire has been raised within the IERS Gazette on whether the leap second should be abolished.
• The string 'Clock: inserting leap second' is found in kernel/time/ntp.c:143 of the 2.6.28 linux kernel.
• The unix localtime() function did not cater for the leap seconds. This was fixed by vendors who applied the Olson time libraries.